From: | Simon Riggs <simon(at)2ndquadrant(dot)com> |
---|---|
To: | Alvaro Herrera <alvherre(at)commandprompt(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Gregory Stark <stark(at)enterprisedb(dot)com>, Heikki Linnakangas <heikki(at)enterprisedb(dot)com>, Neil Conway <neilc(at)samurai(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: advancing snapshot's xmin |
Date: | 2008-03-28 14:07:55 |
Message-ID: | 1206713275.4285.1665.camel@ebony.site |
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Lists: | pgsql-hackers |
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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