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Home Backend Development PHP Tutorial 数据库什么时候用排它锁,排它锁真的效率低吗,效率低怎么办?

数据库什么时候用排它锁,排它锁真的效率低吗,效率低怎么办?

Jun 06, 2016 pm 08:31 PM
mysql php sql

RT,数据库什么时候用排它锁,排它锁真的效率低吗,效率低怎么办?

回复内容:

RT,数据库什么时候用排它锁,排它锁真的效率低吗,效率低怎么办?

数据修改操作的时候建议上X锁,例如 INSERT、UPDATE 或 DELETE。确保不会同时同一资源进行多重更新。
效率和安全性毕竟不可兼得,自己取舍啦

可以改用类似Memcached的CAS(Check And Set)冲突检测机制.
http://php.net/manual/zh/memcached.cas.php

获取数据时,获取用户的余额和版本号(表里面有一个版本号字段version):

<code>SELECT balance, version FROM user WHERE id=1 AND balance>10;
</code>
Copy after login

更新数据时,更新对应用户ID和获取数据时的版本号的数据.
符合条件,则更新余额,并把版本号+1.
不符合条件,则说明这条数据被更新过,所以本次操作无效.

<code>UPDATE user SET balance=balance-10, version=last_version+1 
WHERE id=1 AND version=last_version;
</code>
Copy after login

注意到UPDATE里的last_version为SELECT获取的本次操作的版本号.

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