事务 - mysql共享锁lock in share mode的实际使用场景

Question

看了MySQL的官方文档: 关于锁定对象的部分 分两种锁共享锁: SELECT ... LOCK IN SHARE MODE排它锁: SELECT ... FOR UPDATE 其中排他锁这个场景大家都知道, 就是多个session的事务要对同一个表的一/多条数据进行更...

天蓬老师 · Answer

It is indeed like this, LOCK IN SHARE MODE是读锁(只是不让别人写)，FOR UPDATEIt is a write lock (it does not allow others to add a read lock), Upgrading the read lock to a write lock may cause a deadlock(But downgrading the write lock to a read lock will not, I really don’t Know how MySQL degrades locks), so the timeout issue needs to be considered in the program (either retry or give up).

So in most cases, if there is an UPDATE action after SELECT, you will generally use FOR UPDATE instead of LOCK IN SHARE MODE.