MongoDB (Single-Server) Data Durability Guide

yaofang123

<span class="Apple-style-span" style="color: rgb(85, 85, 85); font-family: Georgia, serif; font-size: 16px; line-height: 24px; background-color: rgb(255, 255, 255); "><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">If you are a MongoDB user or just interested in NoSQL databases in general, you may have seen the excellent “<a href="http://www.mikealrogers.com/2010/07/mongodb-performance-durability/" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">MongoDB has poor data durability by default!</a>” (I am paraphrasing) conversation started by Mikeal Rogers.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">It is an excellent topic to bring up and regardless of Mikeal’s association (he’s a CouchDB developer) I never once got the impression that he was setting up&nbsp;<a href="http://en.wikipedia.org/wiki/Straw_man" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">a straw man</a>&nbsp;to knock it back down; he brought up some really excellent points about how MongoDB favors performance over single-server data durability&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">by default</em>&nbsp;which in turn spurred a great conversation between him, the MongDB/<a href="http://www.10gen.com/team" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">10gen team</a>&nbsp;and some users from the community.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">In this guide I want to outline a number of ways you can increase your single-server durability using MongoDB as well as some optional safer driver behaviors you can make use of to ensure fsync’ing as well as synchronous writes and lastly a tip on keeping your data more aggressively synced across all the nodes in your MongoDB cluster.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); "><strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">REMINDER</strong>:&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">Before getting started, please note that any use of ‘fsync’ syncs all<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">pending</strong>&nbsp;changes and not just the last change made.</em></p><ol style="margin-top: 0px; margin-right: 0px; margin-bottom: 15px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 30px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: none; list-style-position: initial; list-style-image: initial; background-position: initial initial; background-repeat: initial initial; "><li style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: decimal; background-position: initial initial; background-repeat: initial initial; "><a href="http://www.thebuzzmedia.com/mongodb-single-server-data-durability-guide/#overview" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">MongoDB Durability Overview</a></li><li style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: decimal; background-position: initial initial; background-repeat: initial initial; "><a href="http://www.thebuzzmedia.com/mongodb-single-server-data-durability-guide/#cli" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">fsync’ing MongoDB – from the command line</a></li><li style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: decimal; background-position: initial initial; background-repeat: initial initial; "><a href="http://www.thebuzzmedia.com/mongodb-single-server-data-durability-guide/#shell" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; 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background-repeat: initial initial; "><a href="http://www.thebuzzmedia.com/mongodb-single-server-data-durability-guide/#driver" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">fsync’ing MongoDB – from a database driver</a></li><li style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: decimal; background-position: initial initial; background-repeat: initial initial; "><a href="http://www.thebuzzmedia.com/mongodb-single-server-data-durability-guide/#getlasterror" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">MongoDB Synchronous Writes – getLastError</a></li><li style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: decimal; background-position: initial initial; background-repeat: initial initial; "><a href="http://www.thebuzzmedia.com/mongodb-single-server-data-durability-guide/#writeconcern" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">MongoDB Synchronous Writes – Write Concern</a></li><li style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: decimal; background-position: initial initial; background-repeat: initial initial; "><a href="http://www.thebuzzmedia.com/mongodb-single-server-data-durability-guide/#nodes" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">BONUS: “fsync’ing” MongoDB (1.5+) – across multiple servers</a></li><li style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: decimal; background-position: initial initial; background-repeat: initial initial; "><a href="http://www.thebuzzmedia.com/mongodb-single-server-data-durability-guide/#help" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">HELP: How can I fixed a corrupted MongoDB database?</a></li><li style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: decimal; background-position: initial initial; background-repeat: initial initial; "><a href="http://www.thebuzzmedia.com/mongodb-single-server-data-durability-guide/#conclusion" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">Conclusion</a></li><li style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: decimal; background-position: initial initial; background-repeat: initial initial; "><a href="http://www.thebuzzmedia.com/mongodb-single-server-data-durability-guide/#ref" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">MongoDB 1.4 Command Line Reference</a></li></ol><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); "><a name="overview" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "></a></p>MongoDB Durability Overview<p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">The ensuing conversation between Mikeal and the MongoDB/<a href="http://www.10gen.com/team" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">10gen team</a>,&nbsp;like Mike and Kristina, was hugely valuable. If this type of conversation interests you as much as it does me, you can follow this thread “<a href="http://groups.google.com/group/mongodb-user/browse_thread/thread/e4fa92b800d507b2" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">How&nbsp;reliable&nbsp;has MongoDB become?</a>” and my own thread “<a href="http://groups.google.com/group/mongodb-user/browse_thread/thread/afed1f6ba6811c1f#" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">How is a corrupt master repaired from a slave?</a>” for more replies on the subject.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">The MongoDB data-durability highlights that have come out of these conversations so far are:</p><ul style="margin-top: 0px; margin-right: 0px; margin-bottom: 15px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 30px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: none; list-style-position: initial; list-style-image: initial; background-position: initial initial; background-repeat: initial initial; "><li style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: disc; background-position: initial initial; background-repeat: initial initial; ">MongoDB is not designed around single-server durability, but rather&nbsp;<a href="http://blog.mongodb.org/post/381927266/what-about-durability" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">multi-server durability</a>.</li><li style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: disc; background-position: initial initial; background-repeat: initial initial; ">For better&nbsp;<a href="http://www.mongodb.org/display/DOCS/Durability+and+Repair#DurabilityandRepair-SingleServerDurability" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">single-server durability</a>&nbsp;(at the cost of performance) you&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">can</em>&nbsp;configure MongoDB to&nbsp;<a href="http://www.mongodb.org/display/DOCS/fsync+Command" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">fsync at differing intervals</a>&nbsp;(we’ll show you how below).</li><li style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: disc; background-position: initial initial; background-repeat: initial initial; ">MongoDB will add support for better single-server durability&nbsp;<a href="http://groups.google.com/group/mongodb-user/browse_thread/thread/afed1f6ba6811c1f#" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">in dev stream 1.7 and released to production in 1.8</a>&nbsp;(<a href="http://jira.mongodb.org/browse/SERVER-980" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">Issue #980</a>). At the time of this writing it isn’t clear if this will be a “transaction log” style solution as mentioned on Mikeal’s blog comments, or if it will be some other strategy. 10gen hasn’t spec’ed it out yet.</li><li style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: disc; background-position: initial initial; background-repeat: initial initial; ">The upcoming “<a href="http://www.mongodb.org/display/DOCS/Replica+Sets" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">Replica Sets</a>” feature in MongoDB 1.5 (dev) and eventually 1.6 (production) are intended to fully address the problem of creating a high-availability cluster (2 or more) of MongoDB instances that all work together to keep the cluster operational with things like automatic failover and data recovery when a node is brought back online. For multi-server setups,&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">this</em>&nbsp;is what you want to care about.</li></ul><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Mongo’s core strategy of data reliability is still focused around the multi-server setup, but it is nice to see the addition of the “transaction log” going in to the server to help with single-server resilience.<br><a name="cli" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "></a></p>fsync’ing MongoDB – from the command line<p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">On the topic of single-server resilience, the best thing you can&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">currently</em>&nbsp;do (until transaction log support is added) is to increase the number of times you have MongoDB&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">fsync</strong>.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); "><a href="http://en.wikipedia.org/wiki/Fsync" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">fsync</a>‘ing is an operating-system level operation that gets data out of volatile caches and commits it to the disk. Out of the box MongoDB performs an fsync every 60 seconds. What this means for you is that in a&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">worst-case</strong>&nbsp;scenario, like a power outage, your server can loose up to 59.99 seconds worth of data (NOTE: I realize in a real worst-case scenario it could be more due to disk failure, but let’s keep this example manageable).</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">If you are working on a write-heavy server that does thousands of writes a second, loosing 59.99 seconds worth of data could be millions of records. If you deem this too heavy of a loss, you can modify how frequently MongoDB fsync’s to disk by using the&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">–syncdelay=SECONDS</strong>&nbsp;command line argument like so:</p><div class="wp_syntax" style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.5em; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 1px; border-right-width: 1px; border-bottom-width: 1px; border-left-width: 1px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: rgb(249, 249, 249); color: rgb(17, 0, 0); border-top-style: solid; border-right-style: solid; border-bottom-style: solid; border-left-style: solid; border-top-color: silver; border-right-color: silver; border-bottom-color: silver; border-left-color: silver; overflow-x: auto; overflow-y: hidden; width: 610px; background-position: initial initial; background-repeat: initial initial; "><div class="code" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 2px; padding-right: 4px; padding-bottom: 2px; padding-left: 4px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: top; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">mongod <span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(102, 0, 51); background-position: initial initial; background-repeat: initial initial; ">--syncdelay</span>=<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 0, 0); background-position: initial initial; background-repeat: initial initial; ">5</span></div></div><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Which will force the server to flush it’s caches to disk every 20 seconds regardless of what is going on.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">While this might seem like a good idea, you could imagine in a high-activity production environment, fsyncing every few seconds regardless of the operation being performed and how heavy of a load the DB is under might be a bit too heavy handed; you might want to control exactly&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">which</em>&nbsp;operations get fsync’ed to disk and which ones don’t.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Luckily, you can do that!<br><a name="shell" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "></a></p>fsync’ing MongoDB – from the command shell<p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">As it turns out, MongoDB also has an internal “fsync” command you can execute from the MongoDB shell like so:</p><div class="wp_syntax" style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.5em; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 1px; border-right-width: 1px; border-bottom-width: 1px; border-left-width: 1px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: rgb(249, 249, 249); color: rgb(17, 0, 0); border-top-style: solid; border-right-style: solid; border-bottom-style: solid; border-left-style: solid; border-top-color: silver; border-right-color: silver; border-bottom-color: silver; border-left-color: silver; overflow-x: auto; overflow-y: hidden; width: 610px; background-position: initial initial; background-repeat: initial initial; "><div class="code" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 2px; padding-right: 4px; padding-bottom: 2px; padding-left: 4px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: top; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">use admin
db.runCommand<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(122, 8, 116); font-weight: bold; background-position: initial initial; background-repeat: initial initial; ">(</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(122, 8, 116); font-weight: bold; background-position: initial initial; background-repeat: initial initial; ">{</span>fsync:<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 0, 0); background-position: initial initial; background-repeat: initial initial; ">1</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(122, 8, 116); font-weight: bold; background-position: initial initial; background-repeat: initial initial; ">}</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(122, 8, 116); font-weight: bold; background-position: initial initial; background-repeat: initial initial; ">)</span>;</div></div><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">While will execute the fsync&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">synchronously</em>, waiting for it to complete before returning control back to the shell. If you would like to execute the fsync&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">asynchronously</em>&nbsp;which fires the command into the DB but then returns control back to the shell immediately, you can use the optional&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">async:true</strong>&nbsp;argument:</p><div class="wp_syntax" style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.5em; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 1px; border-right-width: 1px; border-bottom-width: 1px; border-left-width: 1px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: rgb(249, 249, 249); color: rgb(17, 0, 0); border-top-style: solid; border-right-style: solid; border-bottom-style: solid; border-left-style: solid; border-top-color: silver; border-right-color: silver; border-bottom-color: silver; border-left-color: silver; overflow-x: auto; overflow-y: hidden; width: 610px; background-position: initial initial; background-repeat: initial initial; "><div class="code" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 2px; padding-right: 4px; padding-bottom: 2px; padding-left: 4px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: top; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">use admin
db.runCommand<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(122, 8, 116); font-weight: bold; background-position: initial initial; background-repeat: initial initial; ">(</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(122, 8, 116); font-weight: bold; background-position: initial initial; background-repeat: initial initial; ">{</span>fsync:<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 0, 0); background-position: initial initial; background-repeat: initial initial; ">1</span>,async:<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(194, 12, 185); font-weight: bold; background-position: initial initial; background-repeat: initial initial; ">true</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(122, 8, 116); font-weight: bold; background-position: initial initial; background-repeat: initial initial; ">}</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(122, 8, 116); font-weight: bold; background-position: initial initial; background-repeat: initial initial; ">)</span>;</div></div><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); "><strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">NOTE</strong>:&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">These examples are straight out of the&nbsp;<a href="http://www.mongodb.org/display/DOCS/fsync+Command" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">MongoDB fsync documentation</a>.</em></p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">This is all well and good, but what about executing these commands from a driver connected to DB instead of needing to always have the Mongo shell up?</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Great news, you can do that too!<br><a name="driver" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "></a></p>fsync’ing MongoDB – from a database driver<p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">MongoDB’s&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">fsync</em>&nbsp;functionality can be invoked from almost all of the&nbsp;<a href="http://www.mongodb.org/display/DOCS/Drivers" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">DB drivers supported</a>, we will focus on the&nbsp;<a href="http://www.mongodb.org/display/DOCS/Java+Language+Center" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">Java MongoDB driver</a>.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Invoking the ‘fsync’ command from the MongoDB drivers is as easy as executing the “<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">fsync:1</strong>” command. In the case of the Java driver, you can use the<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "><a href="http://api.mongodb.org/java/2.0/com/mongodb/DB.html#command(com.mongodb.DBObject)" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">com.mongodb.DB.command(DBObject)</a></em>&nbsp;or&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "><a href="http://api.mongodb.org/java/2.0/com/mongodb/DB.html#command(java.lang.String)" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">com.mongodb.DB.command(String)</a></em>methods. Using the String-based method is the easiest to write an example for and would look like:</p><div class="wp_syntax" style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.5em; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 1px; border-right-width: 1px; border-bottom-width: 1px; border-left-width: 1px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: rgb(249, 249, 249); color: rgb(17, 0, 0); border-top-style: solid; border-right-style: solid; border-bottom-style: solid; border-left-style: solid; border-top-color: silver; border-right-color: silver; border-bottom-color: silver; border-left-color: silver; overflow-x: auto; overflow-y: hidden; width: 610px; background-position: initial initial; background-repeat: initial initial; "><div class="code" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 2px; padding-right: 4px; padding-bottom: 2px; padding-left: 4px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: top; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">DB conn <span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">=</span> Mongo.<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 102, 51); background-position: initial initial; background-repeat: initial initial; ">connect</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">(</span>...<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">)</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">;</span>
conn.<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 102, 51); background-position: initial initial; background-repeat: initial initial; ">command</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">(</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 0, 255); background-position: initial initial; background-repeat: initial initial; ">"{fsync:1}"</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">)</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">;</span></div></div><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">You could imagine in any Java web app you could write a simpler utility method that fired off a sync command that you could call after any important write operation; allowing you to dictate when the server took it’s time to block and fsync or not.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">For example, maybe after user-registration you would fsync to ensure (as best as you can) that the user account is safe and user-registration occurs infrequently enough that you wouldn’t be causing that many locks on the DB to impact performance. But in the case of say users commenting on something, you would avoid fsync’ing because it happens frequently and loosing a comment or two isn’t that bad.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Now the next logical comment likely on the tip of your brain is “That’s cool, but what about synchronous writing that I&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">know</strong>&nbsp;is safe on the server before I continue?”</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">And you know, today is your lucky day, because that’s the next section!</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); "><a name="getlasterror" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "></a></p>MongoDB Synchronous Writes – getLastError<p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">I think we have beaten to death the different ways you can ensure MongoDB keeps its internal cache’s consistent with persisted data on disk using fsync. Parallel to the concerns of fsync’ing is the idea of synchronous writes. More specifically, by default MongoDB operates in a “write and forget” mode to callers. You perform a write operation from a MongoDB driver and the call immediately returns, with you putting your trust in MongoDB that it got the write request and will successfully service it.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">MongoDB behaving like this as&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">a default</strong>&nbsp;is a great idea in my opinion. Assuming, by default, that MongoDB won’t explode into flames and will service your request makes sense when you consider the performance benefits.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">For more important data that cannot be write-and-forgot-ted-ded, MongoDB can optionally support synchronous writes to the DB by way of the “<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "><a href="http://www.mongodb.org/display/DOCS/Last+Error+Commands" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">getLastError</a></strong>” command.&nbsp;The&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">getLastError</strong>&nbsp;command does exactly what you think it would: it gets the last error that occurred for the last operation issued&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">for that connection</strong>&nbsp;(it operates on a per-connection scope).</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Keeping a connection to the DB open and using the&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">getLastErrror</strong>&nbsp;command immediately after a write has the effect of blocking until&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">getLastError</strong>&nbsp;returns a result to the caller.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Different drivers implement the support for&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">getLastError</strong>&nbsp;differently; the Python driver adds support for a&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">boolean</em>&nbsp;value to write operations causing the call to block automatically until complete; the Java driver (because it pools connections) requires you to&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">tell it</em>&nbsp;when you want to keep a particular connection open until you are done with it by way of the&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "><a href="http://api.mongodb.org/java/2.0/com/mongodb/DB.html#requestStart()" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">com.mongodb.DB.requestStart()</a></em>&nbsp;marking method and matching<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "><a href="http://api.mongodb.org/java/2.0/com/mongodb/DB.html#requestDone()" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">com.mongodb.DB.requestDone()</a></em>&nbsp;method.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); "><strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">REMINDER</strong>:&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">While the requestStart and requestDone methods seem like transaction delimiters, they aren’t. They are just marker methods used by the MongoDB Java driver to ensure that subsequent calls get serviced through the same pooled MongoDB connection and not cycled over to another pooled connection</em>.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Using the Java driver as an example, to ensure that our commands go to the same connection (as required by&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">getLastError</strong>) our code would look something like this for a synchronous write:</p><div class="wp_syntax" style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.5em; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 1px; border-right-width: 1px; border-bottom-width: 1px; border-left-width: 1px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: rgb(249, 249, 249); color: rgb(17, 0, 0); border-top-style: solid; border-right-style: solid; border-bottom-style: solid; border-left-style: solid; border-top-color: silver; border-right-color: silver; border-bottom-color: silver; border-left-color: silver; overflow-x: auto; overflow-y: hidden; width: 610px; background-position: initial initial; background-repeat: initial initial; "><div class="code" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 2px; padding-right: 4px; padding-bottom: 2px; padding-left: 4px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: top; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">DB conn <span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">=</span> Mongo.<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 102, 51); background-position: initial initial; background-repeat: initial initial; ">connect</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">(</span>...<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">)</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">;</span>
&nbsp;
conn.<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 102, 51); background-position: initial initial; background-repeat: initial initial; ">requestStart</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">(</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">)</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">;</span>
<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(102, 102, 102); font-style: italic; background-position: initial initial; background-repeat: initial initial; ">// At this point, all commands will be issued through</span>
<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(102, 102, 102); font-style: italic; background-position: initial initial; background-repeat: initial initial; ">// the same connection from the internal Mongo driver</span>
<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(102, 102, 102); font-style: italic; background-position: initial initial; background-repeat: initial initial; ">// connection pool</span>
&nbsp;
conn.<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 102, 51); background-position: initial initial; background-repeat: initial initial; ">getCollection</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">(</span>...<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">)</span>.<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 102, 51); background-position: initial initial; background-repeat: initial initial; ">insert</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">(</span>...<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">)</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">;</span>
CommandResult result <span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">=</span> conn.<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 102, 51); background-position: initial initial; background-repeat: initial initial; ">getLastError</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">(</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">)</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">;</span>
&nbsp;
<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(102, 102, 102); font-style: italic; background-position: initial initial; background-repeat: initial initial; ">// Handle a failure case from result arg</span>
conn.<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 102, 51); background-position: initial initial; background-repeat: initial initial; ">requestDone</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">(</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">)</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">;</span>
&nbsp;
<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(102, 102, 102); font-style: italic; background-position: initial initial; background-repeat: initial initial; ">// Now the Java driver will stop shuffling all commands</span>
<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(102, 102, 102); font-style: italic; background-position: initial initial; background-repeat: initial initial; ">// over that same connection and return it to the pool.</span></div></div><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Again, I could imagine utility classes in a web app that provide synchronous writes to Mongo by wrapping these implementation details in a method like “<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">DAO.saveUser(User user, boolean synchronous)</em>” or something like that.<br><a name="writeconcern" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "></a></p>MongoDB Synchronous Writes – Write Concern<p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">This tip is for the&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">MongoDB Java Driver</strong>&nbsp;folks out there; I don’t know if the other drivers support this, but the examples below apply to the Java driver.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">At both the&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">database</em>&nbsp;and&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">collection</em>&nbsp;level, MongoDB’s Java driver supports&nbsp;<a href="http://api.mongodb.org/java/2.0/com/mongodb/DB.html#setWriteConcern(com.mongodb.DB.WriteConcern)" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">setting</a>&nbsp;a<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "><a href="http://api.mongodb.org/java/2.0/com/mongodb/DB.WriteConcern.html" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">WriteConcern</a></strong>&nbsp;value (values: NONE, NORMAL, STRICT) that indicates to the DB how it should implicitly handle write operations.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">So if you need&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">all</em>&nbsp;your commands against a MongoDB source to be synchronous, you can simply set the WriteConcern on the entire DB connection to be<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "><a href="http://api.mongodb.org/java/2.0/com/mongodb/DB.WriteConcern.html#STRICT" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">com.mongodb.DB.WriteConcern.STRICT</a></em>&nbsp;and not worry about handling<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">requestStart()</em>&nbsp;and&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">requestDone()</em>&nbsp;calls manually as mentioned above.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); "><strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">NOTE</strong>:&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">If you still want to retrieve the&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">getLastError</strong>&nbsp;value to process it, you will still need to use the code from the previous tip to denote to the Java driver that you want to share the same connection for all the commands so the error retrieved is appropriate for the command you issued.</em></p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">You might be wondering why use&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">WriteConcern</strong>&nbsp;at all if the previous tip does the same thing? Well, I think that depends on you.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">If you’d prefer the driver did everything for you as far as managing your synchronicity, then use a&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">WriteConcern</strong>&nbsp;setting; if you’d rather manage it via your own API calls that you can refactor and modify later, then use the previous tip.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">The choice is up to you.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); "><a name="nodes" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "></a></p>BONUS: “fsync’ing” MongoDB (1.5+) – across multiple servers<p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Our last bonus tip for this guide is not a single-server tip, but is so closely related to the topic of data durability that we decided to include it.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">In the world of MongoDB it is common to have a few Mongo servers setup to run together; for example, in a&nbsp;<a href="http://www.mongodb.org/display/DOCS/Master+Slave" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">Master-Slave configuration</a>. Given that this entire guide has been about data durability, the topic of data consistency (in Mongo-land) can be the next question on your lips and we are going to give you a tip on how to manage that across multiple MongoDB nodes.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">This guide so far has been talking about “fsync’ing” a single-server MongoDB’s cache to disk to persist your data (as well as synchronous writes); but, what if you wanted to effectively “fsync” your written data across&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">multiple MongoDB nodes</em>&nbsp;and not just to the disk of a single server?</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Never fear, I shall tell you!</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); "><strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">REMINDER</strong>:&nbsp;<em style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">This tip requires MongoDB 1.5.0 or higher.</em></p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">This&nbsp;<a href="http://www.mongodb.org/display/DOCS/Replication#Replication-ReplicationAcknowledgementviagetlasterror" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">replication acknowledgement command</a>&nbsp;is actually an extension of the already-helpful&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "><a href="http://www.thebuzzmedia.com/mongodb-single-server-data-durability-guide/#getlasterror" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">getLastError</a></strong><a href="http://www.thebuzzmedia.com/mongodb-single-server-data-durability-guide/#getlasterror" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">&nbsp;command we covered above</a>&nbsp;in the form of an optional argument: “w”.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Yep, just the letter “w”.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">The way you use this command is to issue the&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">getLastError</strong>&nbsp;command as you’ve already learned how to do, but include an additional “w” argument with a value &gt; 2 where “w” represents the&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">number of servers in your cluster to force the replication to</strong>, how cool is that?</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">An example usage would look like this:</p><div class="wp_syntax" style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.5em; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 1px; border-right-width: 1px; border-bottom-width: 1px; border-left-width: 1px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: rgb(249, 249, 249); color: rgb(17, 0, 0); border-top-style: solid; border-right-style: solid; border-bottom-style: solid; border-left-style: solid; border-top-color: silver; border-right-color: silver; border-bottom-color: silver; border-left-color: silver; overflow-x: auto; overflow-y: hidden; width: 610px; background-position: initial initial; background-repeat: initial initial; "><div class="code" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 2px; padding-right: 4px; padding-bottom: 2px; padding-left: 4px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: top; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">DB conn <span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">=</span> Mongo.<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 102, 51); background-position: initial initial; background-repeat: initial initial; ">connect</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">(</span>...<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">)</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">;</span>
&nbsp;
conn.<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 102, 51); background-position: initial initial; background-repeat: initial initial; ">requestStart</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">(</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">)</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">;</span> <span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(102, 102, 102); font-style: italic; background-position: initial initial; background-repeat: initial initial; ">// ensure same connection</span>
&nbsp;
conn.<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 102, 51); background-position: initial initial; background-repeat: initial initial; ">getCollection</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">(</span>...<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">)</span>.<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 102, 51); background-position: initial initial; background-repeat: initial initial; ">insert</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">(</span>...<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">)</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">;</span>
conn.<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 102, 51); background-position: initial initial; background-repeat: initial initial; ">getCollection</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">(</span>...<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">)</span>.<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 102, 51); background-position: initial initial; background-repeat: initial initial; ">remove</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">(</span>...<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">)</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">;</span>
&nbsp;
<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(102, 102, 102); font-style: italic; background-position: initial initial; background-repeat: initial initial; ">// Now force the write operation to complete across</span>
<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(102, 102, 102); font-style: italic; background-position: initial initial; background-repeat: initial initial; ">// at least 2 nodes before returning.</span>
conn.<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 102, 51); background-position: initial initial; background-repeat: initial initial; ">command</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">(</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 0, 255); background-position: initial initial; background-repeat: initial initial; ">"{getlasterror: 1, w: 2}"</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">)</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">;</span>
&nbsp;
conn.<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 102, 51); background-position: initial initial; background-repeat: initial initial; ">requestDone</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">(</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(0, 153, 0); background-position: initial initial; background-repeat: initial initial; ">)</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(51, 153, 51); background-position: initial initial; background-repeat: initial initial; ">;</span> <span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(102, 102, 102); font-style: italic; background-position: initial initial; background-repeat: initial initial; ">// release connection</span></div></div><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">This is one of the more powerful additions in MongoDB 1.5+, allowing developers to have direct control over how important data is handled by the servers. You could imagine in a cluster of 10 MongoDB servers, if a new user registers and you don’t want them to continue on into the system until that user account exists on all the servers, how handy this operation can become.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Again, wrapping this in a utility class to make using it easier is probably the way to go.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); "><strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">Update #1</strong>: Kristina from the MongoDB team has provided&nbsp;<a href="http://www.thebuzzmedia.com/mongodb-single-server-data-durability-guide/comment-page-1/#comment-29474" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">PHP and Perl code examples</a>&nbsp;for this tip, thanks!</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); "><a name="help" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "></a></p>HELP: How can I fix a corrupted MongoDB database?<p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">As part of this data-durability conversation around MongoDB, a sub-conversation around&nbsp;<a href="http://groups.google.com/group/mongodb-user/browse_thread/thread/e4fa92b800d507b2/22a56bedfb44be87" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">MongoDB database corruption and repair</a>&nbsp;has sprung up.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Some take-aways from this sub-conversation is:</p><ul style="margin-top: 0px; margin-right: 0px; margin-bottom: 15px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 30px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: none; list-style-position: initial; list-style-image: initial; background-position: initial initial; background-repeat: initial initial; "><li style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: disc; background-position: initial initial; background-repeat: initial initial; ">GOOD: Using&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">CTRL-C</strong>&nbsp;to&nbsp;<a href="http://www.mongodb.org/display/DOCS/Starting+and+Stopping+Mongo" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">shutdown MongoDB</a>&nbsp;is the&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">preferred method</strong>, it produces a&nbsp;<a href="http://www.thebuzzmedia.com/wp-content/uploads/2010/07/mongo-db-clean-shutdown-sequence.png" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">clean shutdown sequence</a>&nbsp;(Picture by Sam Millman).</li><li style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: disc; background-position: initial initial; background-repeat: initial initial; ">GOOD: Sending&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">SIGINT</strong>&nbsp;or&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">SIGTERM</strong>&nbsp;signals to the MongoDB process is the same as using CTRL-C; it produces a&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">clean shutdown sequence</strong>.</li><li style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; list-style-type: disc; background-position: initial initial; background-repeat: initial initial; ">BAD: Sending&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">KILL</strong>&nbsp;or&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">kill -9</strong>&nbsp;signals to the MongoDB process will&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">likely corrupt the database</strong>&nbsp;as MongoDB cannot shut down cleanly.</li></ul><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">All that being said, in the off-chance that you have a power outage and your MongoDB database gets corrupted, the correct way to repair it is using the&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "><a href="http://www.mongodb.org/display/DOCS/Durability+and+Repair#DurabilityandRepair-RepairCommand" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">repair</a></strong><a href="http://www.mongodb.org/display/DOCS/Durability+and+Repair#DurabilityandRepair-RepairCommand" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">&nbsp;command</a>.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">You can use the&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">repair</strong>&nbsp;command directly from the command line, like so:</p><div class="wp_syntax" style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.5em; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 1px; border-right-width: 1px; border-bottom-width: 1px; border-left-width: 1px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: rgb(249, 249, 249); color: rgb(17, 0, 0); border-top-style: solid; border-right-style: solid; border-bottom-style: solid; border-left-style: solid; border-top-color: silver; border-right-color: silver; border-bottom-color: silver; border-left-color: silver; overflow-x: auto; overflow-y: hidden; width: 610px; background-position: initial initial; background-repeat: initial initial; "><div class="code" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 2px; padding-right: 4px; padding-bottom: 2px; padding-left: 4px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: top; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">mongod <span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(102, 0, 51); background-position: initial initial; background-repeat: initial initial; ">--repair</span></div></div><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">or you can execute it from inside the MongoDB shell, like so:</p><div class="wp_syntax" style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.5em; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 1px; border-right-width: 1px; border-bottom-width: 1px; border-left-width: 1px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: rgb(249, 249, 249); color: rgb(17, 0, 0); border-top-style: solid; border-right-style: solid; border-bottom-style: solid; border-left-style: solid; border-top-color: silver; border-right-color: silver; border-bottom-color: silver; border-left-color: silver; overflow-x: auto; overflow-y: hidden; width: 610px; background-position: initial initial; background-repeat: initial initial; "><div class="code" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 2px; padding-right: 4px; padding-bottom: 2px; padding-left: 4px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: top; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">db.repairDatabase<span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(122, 8, 116); font-weight: bold; background-position: initial initial; background-repeat: initial initial; ">(</span><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 12px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(122, 8, 116); font-weight: bold; background-position: initial initial; background-repeat: initial initial; ">)</span>;</div></div><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">In either case, the repair operation will cycle through the disk contents and repair the corrupted portions of your file.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); "><strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "><span style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(255, 0, 0); background-position: initial initial; background-repeat: initial initial; ">IMPORTANT</span>: This can result in loss of corrupted data.</strong></p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">To clarify, you have no other choice. Your database is already messed up, running the<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">repair</strong>&nbsp;command will get it back into a&nbsp;serviceable&nbsp;state, but that could include pruning data from your database that is corrupted. Just because you run repair doesn’t mean the world will automatically be&nbsp;rosy&nbsp;again, you have to always take 2nd and 3rd level precautions against data-loss.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">To help cover anyone in a multi-server jam, in a Master/Slave setup where the Master fails and your Slave continues chugging along, you have to forget about recovering the Master and promote the Slave to the Master and then bing the old-Master back online as a Slave (switch their roles). At which point you’ll have to repair the slave to ensure the data store is in good condition, then likely issue an&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">–autoresync</strong>&nbsp;command to get the Slave back up to speed, or a&nbsp;<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">–fastsync</strong>&nbsp;if you have grabbed a disk-snapshot of the master and copied it over to the slave to use as a “starting point” for it’s snapshot.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Either way, data recovery is hairy business. That is why everyone in the MongoDB community is so excited for&nbsp;<a href="http://www.mongodb.org/display/DOCS/Replica+Sets" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; color: rgb(48, 136, 255); text-decoration: none; background-position: initial initial; background-repeat: initial initial; " target="_blank">Replica Sets</a>&nbsp;to show up in 1.6 stable. In that setup, the individual nodes are configured to fail-over between one another and automatically resync themselves either others in the cluster when they come back up; making your life a bit easier.<br><a name="conclusion" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "></a></p>Conclusion<p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">I hope you find this guide helpful. If you have any questions, spot any errors or have recommended additions for the guide, please leave a comment and I’ll take a look.</p><p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Happy (and safe) Mongo’ing!<br><a name="ref" style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "></a></p>MongoDB 1.4 Command Line Reference<p style="margin-top: 0px; margin-right: 0px; margin-bottom: 1.2em; margin-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 16px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; font: normal normal normal 16px/1.5em Georgia, serif; color: rgb(85, 85, 85); ">Below is the full list of command line options for MongoDB 1.4 for easy reference.</p><strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 13px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; "> General options:</strong>
-h [ --help ] &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; show this usage information
--version &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; show version information
-f [ --config ] arg &nbsp; &nbsp; &nbsp; configuration file specifying additional options
-v [ --verbose ] &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;be more verbose (include multiple times for more
verbosity e.g. -vvvvv)
--quiet &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; quieter output
--port arg &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;specify port number
--logpath arg &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; file to send all output to instead of stdout
--logappend &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; append to logpath instead of over-writing
--bind_ip arg &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; local ip address to bind listener - all local ips
bound by default
--dbpath arg (=/data/db/) directory for datafiles
--directoryperdb &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;each database will be stored in a separate directory
--repairpath arg &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;root directory for repair files - defaults to dbpath
--cpu &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; periodically show cpu and iowait utilization
--noauth &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;run without security
--auth &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;run with security
--objcheck &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;inspect client data for validity on receipt
--quota &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; enable db quota management
--quotaFiles arg &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;number of files allower per db, requires --quota
--appsrvpath arg &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;root directory for the babble app server
--nocursors &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; diagnostic/debugging option
--nohints &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; ignore query hints
--nohttpinterface &nbsp; &nbsp; &nbsp; &nbsp; disable http interface
--rest &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;turn on simple rest api
--noscripting &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; disable scripting engine
--noprealloc &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;disable data file preallocation
--smallfiles &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;use a smaller default file size
--nssize arg (=16) &nbsp; &nbsp; &nbsp; &nbsp;.ns file size (in MB) for new databases
--diaglog arg &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 0=off 1=W 2=R 3=both 7=W+some reads
--sysinfo &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; print some diagnostic system information
--upgrade &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; upgrade db if needed
--repair &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;run repair on all dbs
--notablescan &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; do not allow table scans
--syncdelay arg (=60) &nbsp; &nbsp; seconds between disk syncs (0 for never)
--profile arg &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 0=off 1=slow, 2=all
--slowms arg (=100) &nbsp; &nbsp; &nbsp; value of slow for profile and console log
--maxConns arg &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;max number of simultaneous connections
--install &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; install mongodb service
--remove &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;remove mongodb service
--service &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; start mongodb service
<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 13px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">Replication options:</strong>
--master &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;master mode
--slave &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; slave mode
--source arg &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;when slave: specify master as &lt;server:port&gt;
--only arg &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;when slave: specify a single database to replicate
--pairwith arg &nbsp; &nbsp; &nbsp; &nbsp;address of server to pair with
--arbiter arg &nbsp; &nbsp; &nbsp; &nbsp; address of arbiter server
--slavedelay arg &nbsp; &nbsp; &nbsp;specify delay (in seconds) to be used when applying
master ops to slave
--fastsync &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;indicate that this instance is starting from a dbpath
snapshot of the repl peer
--autoresync &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;automatically resync if slave data is stale
--oplogSize arg &nbsp; &nbsp; &nbsp; size limit (in MB) for op log
--opIdMem arg &nbsp; &nbsp; &nbsp; &nbsp; size limit (in bytes) for in memory storage of op ids
<strong style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; padding-top: 0px; padding-right: 0px; padding-bottom: 0px; padding-left: 0px; border-top-width: 0px; border-right-width: 0px; border-bottom-width: 0px; border-left-width: 0px; border-style: initial; border-color: initial; outline-width: 0px; outline-style: initial; outline-color: initial; font-size: 13px; vertical-align: baseline; background-image: initial; background-attachment: initial; background-origin: initial; background-clip: initial; background-color: transparent; background-position: initial initial; background-repeat: initial initial; ">Sharding options:</strong>
--configsvr &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; declare this is a config db of a cluster
--shardsvr &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;declare this is a shard db of a cluster</span>