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Editorial Team
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Asked: 2026-05-18T01:08:58+00:00

I’m getting the following error pretty often when running a certain query in my

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I’m getting the following error pretty often when running a certain query in my database (all tables use the InnoDB storage engine): “Deadlock found when trying to get lock; try restarting transaction”

The query is DELETE FROM sessions WHERE userid != 0 AND lastactivity < 1289594761 AND admin = 1 AND userid NOT IN (SELECT userid FROM users WHERE (userflags & 1048576))

The errors started to occur when I’ve added the NOT IN part to my WHERE statement.
Why is this causing issues and what can I do to prevent this?

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1 Answer

  1. Editorial Team

    An easy solution would be to separate this into two consecutive queries. I.e.,:

    SELECT userid into #tmptable FROM users WHERE (userflags & 1048576);

    DELETE FROM sessions WHERE userid != 0 AND lastactivity < 1289594761 AND admin = 1 AND userid NOT IN (select userid from #tmptable);

    That way you’re working with a local session copy of the values from the second table and not causing a read lock on it. However, this is just a quick-and-dirty solution. A better solution would be to analyze the transaction lock settings from all activities that touch these two tables and to rewrite the query, if you’ll be re-using it regularly.

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