Re: Improvement of procArray.xmin for VACUUM

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Bruce Momjian <bruce(at)momjian(dot)us>
Cc: Simon Riggs <simon(at)2ndquadrant(dot)com>, Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, PostgreSQL-patches <pgsql-patches(at)postgresql(dot)org>
Subject: Re: Improvement of procArray.xmin for VACUUM
Date: 2007-03-27 14:02:39
Message-ID: 19410.1175004159@sss.pgh.pa.us
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Bruce Momjian <bruce(at)momjian(dot)us> writes:
> Tom Lane wrote:
>> Bruce Momjian <bruce(at)momjian(dot)us> writes:
>>> Well, my secondary addition was to start MyProc->xmin with the current
>>> xid counter, rather than your own xid.
>>
>> Don't tell me you seriously believe that would work.

> I do. Please tell me why it will not.

You can't have GlobalXmin greater than your own xid, else log space
(particularly pg_subtrans) may be recycled too soon.

regards, tom lane

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