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How to avoid race condition if multiple clients choose in MySQL?

I have a task_id table that has two columns:

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

Easy if I only use one client (Perl script): pick one unfinished

task id, update it to processing

, process it and update to finished

in a loop.

But I am planning on using multiple clients to accomplish this task. There is a possibility that two clients are taking the entry at the same time, how to avoid it?

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2 answers


If your mysql table engine is INNODB, it will lock that particular row when updating the table record so that another query doesn't conflict with the previous update.



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The update has something like:

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


then check if the update actually changed the entry.

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