Date: Mon, 31 Mar 2014 15:18:07 +0200
From: Andres Freund <andres@2ndquadrant.com>
To: Stephen Frost <sfrost@snowman.net>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, pgsql-hackers@postgresql.org
Subject: Re: MultiXactId error after upgrade to 9.3.4
Message-ID: <20140331131807.GC18358@alap3.anarazel.de>
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On 2014-03-31 09:09:08 -0400, Stephen Frost wrote:
> * Alvaro Herrera (alvherre@2ndquadrant.com) wrote:
> > I guess I wasn't expecting that too-old values would last longer than a
> > full wraparound cycle.  Maybe the right fix is just to have the second
> > check also conditional on allow_old.
> 
> I don't believe this was a wraparound case.

Could you show pg_controldata from the old cluster?

> > Anyway, it's not clear to me why this database has a multixact value of
> > 6 million when the next multixact value is barely above one million.
> > Stephen said a wraparound here is not likely.
> 
> I don't think the xmax value is a multixact at all- I think it's
> actually a regular xid, but everyone is expected to ignore it because
> XMAX_IS_INVALID, yet somehow the MULTIXACT bit was also set and the new
> code expects to be able to look at the xmax field even though it's
> marked as invalid..

XMAX_IS_INVALID was never allowed to be ignored for vacuum AFAICS. So I
don't think this is a valid explanation.

Greetings,

Andres Freund

-- 
 Andres Freund	                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services


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