From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Gregory Stark <stark(at)enterprisedb(dot)com> |
Cc: | "Alvaro Herrera" <alvherre(at)commandprompt(dot)com>, pgsql-patches(at)postgresql(dot)org |
Subject: | Re: Autovacuum cancellation |
Date: | 2007-10-26 00:38:42 |
Message-ID: | 29572.1193359122@sss.pgh.pa.us |
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Lists: | pgsql-committers pgsql-hackers pgsql-patches |
Gregory Stark <stark(at)enterprisedb(dot)com> writes:
> Can autovacuum actually get into a hard deadlock?
It can certainly be part of a deadlock loop, though the practical cases
might be few. It will be holding more than one lock, eg a lock on its
target table and various transient locks on system catalogs, and other
processes taking or trying for exclusive locks on those things could
create issues. I think it's OK to leave the issue go for now, until
we see if anyone hits it in practice --- I just wanted to mention that
we might need to consider the problem in future.
> I think there's a window where the process waiting directly on
> autovacuum could have already fired its deadlock check before it was
> waiting directly on autovacuum.
I think you don't understand what that code is doing. If there's an
autovac anywhere in the dependency graph, it'll find it.
regards, tom lane
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