From: | Andres Freund <andres(at)2ndquadrant(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Bruce Momjian <bruce(at)momjian(dot)us>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, PostgreSQL Bugs <pgsql-bugs(at)postgresql(dot)org> |
Subject: | Re: pg_upgrade < 9.3 -> >=9.3 misses a step around multixacts |
Date: | 2014-07-21 16:48:57 |
Message-ID: | 20140721164857.GO5974@alap3.anarazel.de |
Views: | Raw Message | Whole Thread | Download mbox | Resend email |
Thread: | |
Lists: | pgsql-bugs |
On 2014-07-21 12:43:24 -0400, Tom Lane wrote:
> Andres Freund <andres(at)2ndquadrant(dot)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.
I wonder if GetTopTransactionId()/MultiXactIdSetOldestMember() and using
lastSane* = ReadNew* isn't sufficient. After the xid assignment
concurrent GetOldest* can't go below the ReadNew* values anymore, right?
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
From | Date | Subject | |
---|---|---|---|
Next Message | Tom Lane | 2014-07-21 17:03:21 | Re: pg_upgrade < 9.3 -> >=9.3 misses a step around multixacts |
Previous Message | Tom Lane | 2014-07-21 16:43:24 | Re: pg_upgrade < 9.3 -> >=9.3 misses a step around multixacts |