On Fri, 2008-03-28 at 10:35 -0300, Alvaro Herrera wrote:

> The problem is that we always consider every transaction's PGPROC->xid
> in calculating MyProc->xmin.  So if you have a long running
> transaction, it doesn't matter how far beyond the snapshots are -- the
> value returned by GetOldestXmin will always be at most the old
> transaction's Xid.  Even if that transaction cannot see the old rows
> because all of its snapshots are way in the future.

It may not have a TransactionId yet.

So we should have the capability to prevent long running read-only
transactions from causing a build up of dead row versions. But long
running write transactions would still be a problem.

-- 
  Simon Riggs
  2ndQuadrant  http://www.2ndQuadrant.com 

  PostgreSQL UK 2008 Conference: http://www.postgresql.org.uk

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• Re: advancing snapshot's xmin at 2008-03-28 13:35:10 from Alvaro Herrera

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• Re: advancing snapshot's xmin at 2008-03-28 14:26:34 from Alvaro Herrera

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Next:	From: Alvaro Herrera	Date: 2008-03-28 14:26:34
	Subject: Re: advancing snapshot's xmin
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	Subject: Prereading using posix_fadvise (was Re: Commitfest patches)