A minute teaches you to know the difference between optimistic and pessimistic locks

Pessimistic lock (pessimistic lock), as the name implies, is very pessimistic, every time to take the data when they think others will change, so every time when the data are locked, so that others want to take this data will block until it gets the lock. Traditional relational database in the use of a lot of this locking mechanism, such as row locks, table locks, read locks, write locks, etc., are in operation before the lock.

Optimistic lock (optimistic lock), as the name implies, is very optimistic, every time to take the data when they think others will not be modified, so will not be locked, but in the update will be judged in the period when others have to update this data, you can use the version number and other mechanisms. Optimistic locking is useful for multi-read application types, which can improve throughput, such as the fact that a database provides an optimistic lock similar to the write_condition mechanism.

The two kinds of locks have advantages and disadvantages, not to think of one better than the other, like the optimistic lock for less write, that is, the conflict really rarely occurs, this can save the lock overhead, increase the overall system throughput. However, if there is frequent conflict, the upper application will continue to retry, which is to reduce the performance, so in this case, pessimistic locking is more appropriate.

Original: http://blog.csdn.net/hongchangfirst/article/details/26004335

Author: Hongchangfirst

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