| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Heikki Linnakangas <heikki(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 12:56:37 |
| Message-ID: | 10572.1193403397@sss.pgh.pa.us |
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Heikki Linnakangas <heikki(at)enterprisedb(dot)com> writes:
> Alvaro Herrera wrote:
>> /*
>> * Look for a blocking autovacuum. There will only ever
>> * be one, since the autovacuum workers are careful
>> * not to operate concurrently on the same table.
>> */
> I think that's a bit unaccurate. You could have multiple autovacuum
> workers operating on different tables participating in a deadlock. The
> reason that can't happen is that autovacuum never holds a lock while
> waiting for another.
And that's not true either. It may only want low-grade locks (eg
AccessShareLock on a system catalog) but deadlock is nonetheless
entirely possible in principle.
regards, tom lane
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