| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Merlin Moncure <mmoncure(at)gmail(dot)com> |
| Cc: | Andres Freund <andres(at)2ndquadrant(dot)com>, pgsql-performance(at)postgresql(dot)org, Maciek Sakrejda <m(dot)sakrejda(at)gmail(dot)com>, Claudio Freire <klaussfreire(at)gmail(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, Anibal David Acosta <aa(at)devshock(dot)com> |
| Subject: | Re: how to avoid deadlock on masive update with multiples delete |
| Date: | 2012-10-05 16:21:01 |
| Message-ID: | 10891.1349454061@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
Merlin Moncure <mmoncure(at)gmail(dot)com> writes:
> Can't it be forced like this (assuming it is in fact a vanilla order
> by problem)?
> EXPLAIN DELETE FROM test USING (SELECT g FROM test ORDER BY
> ctid FOR UPDATE) x where x.g = test.g;
> (emphasis on 'for update')
Hm ... yeah, that might work, once you redefine the problem as "get the
row locks in a consistent order" rather than "do the updates in a
consistent order". But I'd be inclined to phrase it as
EXPLAIN DELETE FROM test USING (SELECT ctid FROM test ORDER BY
g FOR UPDATE) x where x.ctid = test.ctid;
I'm not sure that "ORDER BY ctid" is really very meaningful here; think
about FOR UPDATE switching its attention to updated versions of rows.
regards, tom lane
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