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Re: Improvement of procArray.xmin for VACUUM

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(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 14:17:41
Message-ID: 200703271417.l2REHf012470@momjian.us (view raw or flat)
Thread:
Lists: pgsql-patches
Tom Lane wrote:
> 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.

OK, so maybe GlobalXmin would have to be split into two new variables
that control log space and dead-row detection separately.

-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>          http://momjian.us
  EnterpriseDB                               http://www.enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +

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