Re: Postgres Replaying WAL slowly - Mailing list pgsql-performance

From Tom Lane
Subject Re: Postgres Replaying WAL slowly
Date
Msg-id 24455.1404169460@sss.pgh.pa.us
Whole thread Raw
In response to Re: Postgres Replaying WAL slowly  (Jeff Frost <jeff@pgexperts.com>)
Responses Re: Postgres Replaying WAL slowly  (Andres Freund <andres@2ndquadrant.com>)
Re: Postgres Replaying WAL slowly  (Jeff Frost <jeff@pgexperts.com>)
List pgsql-performance
Jeff Frost <jeff@pgexperts.com> writes:
>>> So it seems like we have a candidate explanation.  I'm a bit surprised
>>> that StandbyReleaseLocks would get this slow if there are only a dozen
>>> AccessExclusiveLocks in place at any one time, though.  Perhaps that
>>> was a low point and there are often many more?

> Since we turned on the monitoring for that, we had a peak of 13,550
> AccessExclusiveLocks.

Ah ... that's more like a number I can believe something would have
trouble coping with.  Did you see a noticeable slowdown with this?
Now that we've seen that number, of course it's possible there was an
even higher peak occurring when you saw the trouble.

Perhaps there's an O(N^2) behavior in StandbyReleaseLocks, or maybe
it just takes awhile to handle that many locks.

Did you check whether the locks were all on temp tables of the
ON COMMIT DROP persuasion?

            regards, tom lane


pgsql-performance by date:

Previous
From: Jeff Frost
Date:
Subject: Re: Postgres Replaying WAL slowly
Next
From: Andres Freund
Date:
Subject: Re: Postgres Replaying WAL slowly