为什么lotus邮箱删完邮件还要压缩一下才能释放出硬盘空间？

woshiyiziyu

为什么lotus邮箱删完邮件还要压缩一下才能释放出硬盘空间？
我用的是lotus 8.5的邮箱，每次把废纸篓里的邮件删完了之后，我的邮箱所在的服务器上的硬盘空间并没有释放，只有在我压缩了一下了之后才会释放。不知道lotus文档型数据库为什么会这样，有没有介绍文档型数据库的资料呢，网上Google了半天了。

woshiyiziyu

What is a Notes Database

A Lotus Notes database generally has a file extension of ".nsf". Within that file, there can be data, design elements, and programming code. Each database file also has its own security in the form of an Access Control List (ACL). Visually, you can imagine a Notes database file like this:



A brief discussion of the elements of a database is below.

DATA
The data inside a Notes database is stored as a set of records -- each record is referred to as a Document. The information in a Document consists of one or more fields, which can be in any number of formats. Text, numbers, and dates are the basic data types, but you can also store things like formatted rich text and file attachments in a field.

A Notes database can also access data from other databases. These databases can be other Notes databases, or any kind of database that is accessible via ODBC. In this way, Notes can act as a front-end to other data sets, even relational databases.

DESIGN
Data is available using any of a number of different design elements that are stored in the database. On a basic level, you use Forms to access, modify, and create records/Documents, and Views to sort and categorize data sets into tabular form. There are also things like Navigators and Outlines, that allow you to create visual interfaces to other design elements and aid in navigation.

Virtually all of the design elements in a database can be viewed using either a Notes client or a web browser. The Notes/Domino server can natively translate these things and present them as web pages, which makes it quite easy to turn a Notes database into a web site. A Notes designer can even add web-specific design enhancements like CSS and DHTML to a Form, View, Navigator, etc.

CODE
In order to provide programmatic manipulation of data, a designer can embed many different types of code in a database. Notes has native support for a Formula (macro) language, LotusScript (very similar to Visual Basic), Java, and JavaScript. This code can be placed directly on design elements such as Forms and Views, or it can be placed in modules called Agents.

The code in a database can manipulate data within the database, but it can also interact with the user, the operating system, and external data and processes as well. For example, using LotusScript you can access DLL functions, COM objects, and OLE objects. Using Java, you have a rich set of tools for working with sockets, threads, and GUI components (among other things). Notes even has an exposed API layer that can be accessed via C and C++ libraries.

SECURITY
Wrapped around all of these database elements, Notes provides a strong security layer called an Access Control List (ACL). This allows a database designer or administrator to fine tune what different users are allowed to do within the database. On a global level, users have access types such as "Author", "Editor", and "Designer", which indicate what they are allowed to change within the database. On a slightly more specific level, users can be granted or denied access to do things like delete Documents or create Agents. On a much more granular level, the designer of a database can grant or deny access to Views, Forms, sections of Forms, and even individual Documents based on the ACL.

woshiyiziyu

为什么会这样设计呢？如果一删除邮件就立即去释放硬盘空间的话，那么每清空一次废纸篓，lotus domino就要调用文件系统的API去梳理notes数据库以便释放出空间来，这样一来开销就大了，性能就下降了。以下是猜想：lotus domino在清空废纸篓时不会真的去删除邮件，只是给邮件打上“已删除”的标记，这些已删除的邮件占用的硬盘空间可以被再次利用，而只有等到压缩时邮件所占用的硬盘空间才会得到释放。
那么如果出现提示“邮件大小超过阈值，不能再邮件文件中写入任何内容。请删除消息，清空废纸篓并压缩邮件文件”，只要删除一些邮件并清空废纸篓就可以了，不需要压缩邮件，提示也会消失。

meppy

事实上，你点了compact以后也不会马上看到效果，系统有专门的task去处理compact，还是性能问题，架构而已。

sakulagi

主要是性能方面的考虑。