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Re: Delete query not using index and cause deadlock
Posted by: Rick James
Date: August 22, 2015 03:48PM

I wonder if the _composite_ index
INDEX(grid_id = 10, grid_role_id) would help?

Perhaps it would also require reformulating the query to

    FROM `customgrid_grid_role` t1
    JOIN `customgrid_grid_role` t2  USING (grid_role_id)  -- assuming that is the PK
       WHERE t2.grid_id = 10
         AND t2.grid_role_id NOT IN (...);
(I am not sure of the syntax.)

The hope in my reformulation is that it will do an _index_ scan on t2, then DELETE from t1. This _might_ further avoid the contention.
Øystein, how does that sound?

A different trick is to _sort_ the ids before launching into the DELETE (or other query). That tends to avoid _deadlocks_ by turning them into "waits". The problem with your query is that it's not easy to get the list of ids, much less, to sort them.

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Re: Delete query not using index and cause deadlock
August 22, 2015 03:48PM

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