From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@2ndquadrant.com>
cc: Bruce Momjian <bruce@momjian.us>,
 Alvaro Herrera <alvherre@2ndquadrant.com>,
 PostgreSQL Bugs <pgsql-bugs@postgresql.org>
Subject: Re: pg_upgrade < 9.3 -> >=9.3 misses a step around multixacts
In-reply-to: <20140721163409.GB14989@alap3.anarazel.de>
References: <20140720225653.GG5974@alap3.anarazel.de>
 <18673.1405897470@sss.pgh.pa.us> <18851.1405897900@sss.pgh.pa.us>
 <20140720233125.GI5974@alap3.anarazel.de> <19458.1405899435@sss.pgh.pa.us>
 <20140720234925.GJ5974@alap3.anarazel.de> <22178.1405903964@sss.pgh.pa.us>
 <26504.1405912770@sss.pgh.pa.us> <20140721161222.GA17049@alap3.anarazel.de>
 <3655.1405959656@sss.pgh.pa.us> <20140721163409.GB14989@alap3.anarazel.de>
Comments: In-reply-to Andres Freund <andres@2ndquadrant.com>
 message dated "Mon, 21 Jul 2014 18:34:09 +0200"
Date: Mon, 21 Jul 2014 12:43:24 -0400
Message-ID: <4182.1405961004@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-bugs-owner@postgresql.org

Andres Freund <andres@2ndquadrant.com> writes:
> I'm not wondering so much about vac_update_relstats(). There indeed the
> calls aren't new and the worst that can happen is a slightly older
> freeze limit. I'm more wondering about vac_update_datfrozenxid(). Afaics
> we very well could hit
> 	newFrozenXid = lastSaneFrozenXid = GetOldestXmin(NULL, true);
> 	newMinMulti = lastSaneMinMulti = GetOldestMultiXactId();
> for a relation that has just been vacuumed by another backend.

Hmm ... I see.  The issue is not what the computed minimum datfrozenxid
etc should be; it's right to err in the backwards direction there.
It's whether we want to declare that the calculation is bogus and abandon
truncation if another session manages to sneak in a very-new relfrozenxid.
Yeah, you're right, we need to be conservative about doing that.  I'd
wanted to avoid extra calls here but I guess we have to do them after all.
Will fix.

			regards, tom lane


-- 
Sent via pgsql-bugs mailing list (pgsql-bugs@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-bugs