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Re: Improvement of procArray.xmin for VACUUM

From: Gregory Stark <stark(at)enterprisedb(dot)com>
To: "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: "Heikki Linnakangas" <heikki(at)enterprisedb(dot)com>, "Bruce Momjian" <bruce(at)momjian(dot)us>, "PostgreSQL-patches" <pgsql-patches(at)postgresql(dot)org>
Subject: Re: Improvement of procArray.xmin for VACUUM
Date: 2007-03-24 16:14:53
Message-ID: 874poa62ki.fsf@oxford.xeocode.com (view raw or flat)
Thread:
Lists: pgsql-patches
> OTOH, do we have any evidence that this is worth bothering with at all?
> I fear that the cases of long-running transactions that are problems
> in the real world wouldn't be helped much --- for instance, pg_dump
> wouldn't change behavior because it uses a serializable transaction.
Well I think this would be the same infrastructure we would need to do the
other discussed improvement to address pg_dump's impact. That would require us
to publish the youngest xmax of the live snapshots. Vacuum could deduce that
that xid cannot possibly see any transactions between the youngest extant xmax
and the oldest in-progress transaction.
-- 
  Gregory Stark
  EnterpriseDB          http://www.enterprisedb.com


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Subject: Re: Improvement of procArray.xmin for VACUUM
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