如果几个客户在MySQL中选择，如何避免竞争条件？

Question

I have a task_id table which has two columns:

`tid`:task id,
`state`:0:unfinished,1:processing,2:finished

It's easy if I use only one client(Perl script): fetch one unfinished task id,update it to processing , process it, and update it to finished in a loop.

But I'm planning to use several clients to do the task. There is a chance that two clients fetch a record in the same time, how to avoid it?

Answer 1

如果您的mysql表的引擎是INNODB，那么它会在更新表记录时锁定该特定行，以便其他请求不会与先前的更新冲突。

Answer 2

Have the update be something like:

update task_id set state=1 where tid=? and state=0;

then check if the update actually modified a record.