No update lock on tables ?

jimhongchen

Why do tables have only shared, exclusive, and intent locks, no update lock?

viacocha

什么意思，不明白

jazy

我觉得你这个问题混淆了因和果的关系！
sybase提供了shared, exclusive, and intent locks
但是这些锁是因为各种对表的操作而引起的，比如你执行查询操作，数据库会根据会对表加上一个shared锁，而在执行update 和delete操作时会在执行前加上一个exclusive锁！更详细的关于锁的解释可看看本版精华中的帖子·

jimhongchen

A document says that there are 7 types of locking mechanisms:
1. shared
2. update
3. exclusive
4. intent
5. next key, range infinity key
6. demand
7. latch

These locking mechanisms have 3 applications:
1. Tables: shared, exclusive, intent
2. Pages: shared, update, exclusive, latch
3. Rows: shared, update, exclusive, next key

Therefore I am curious about why there is no update lock mechanism on the Table item above?