Date: Tue, 26 May 2015 12:01:59 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Paul Smith <paul@pscs.co.uk>
Cc: pgsql-hackers@postgresql.org
Subject: Re: ERROR:  MultiXactId xxxx has not been created yet --
 apparent wraparound
Message-ID: <20150526150159.GV5885@postgresql.org>
References: <556439CF.7070109@pscs.co.uk>
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Paul Smith wrote:
> With PostgreSQL 9.3.5 on Ubuntu 12.04, I'm getting the error:
> 
> ERROR:  MultiXactId 1934308693 has not been created yet -- apparent
> wraparound
> 
> on doing various queries on our database. I don't think it is a wraparound -
> I think the tuple has mistakenly decided it has a MultiXactId related to it.

Yeah, that looks like the case.  According to your pg_controldata
output, you haven't used many multixacts at all:

> Latest checkpoint's NextMultiXactId:  216
> Latest checkpoint's NextMultiOffset:  439

and the fact that you only have these files:

> The pg_multixact directory contains two files
> members/0000
> offsets/0000

confirms this.  You XID counter is also rather low, only 24 million:

> Latest checkpoint's NextXID:          0/24005839

so it doesn't seem plausible that the single bit HEAP_XMAX_IS_MULTI was
turned on accidentally (something which I've never seen happen).

It doesn't look like a randomly corrupt page either; normally you would
see errors about mismatching page headers before you get to the point
where Xmax is read.  I wonder if the data page came from elsewhere.
Maybe you copied a data file from another database?

-- 
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services


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