Re: MultiXactId error after upgrade to 9.3.4

From: Andres Freund <andres(at)2ndquadrant(dot)com>
To: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
Cc: Stephen Frost <sfrost(at)snowman(dot)net>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: MultiXactId error after upgrade to 9.3.4
Date: 2014-03-31 11:57:13
Message-ID: 20140331115713.GA18358@alap3.anarazel.de
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On 2014-03-31 08:54:53 -0300, Alvaro Herrera wrote:
> My conclusion here is that some part of the code is failing to examine
> XMAX_INVALID before looking at the value stored in xmax itself. There
> ought to be a short-circuit. Fortunately, this bug should be pretty
> harmless.
>
> .. and after looking, I'm fairly sure the bug is in
> heap_tuple_needs_freeze.

heap_tuple_needs_freeze() isn't *allowed* to look at
XMAX_INVALID. Otherwise it could miss freezing something still visible
on a standby or after an eventual crash.

Greetings,

Andres Freund

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

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