Date: Wed, 23 Apr 2014 16:30:05 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Andres Freund <andres@2ndquadrant.com>
Cc: Bruce Momjian <bruce@momjian.us>, Stephen Frost <sfrost@snowman.net>,
 pgsql-hackers@postgresql.org
Subject: Re: MultiXactId error after upgrade to 9.3.4
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Andres Freund wrote:

> I think this patch is a seriously bad idea. For one, it's not actually
> doing anything about the problem - the tuple can be accessed without
> freezing getting involved.

Normal access other than freeze is not a problem, because other code
paths do check for HEAP_XMAX_INVALID and avoid access to Xmax if that's
set.

> For another, it will increase wall traffic for freezing of short lived
> tuples considerably, without any benefit.

True.  I didn't actually try to run this; it was just for demonstration
purposes.  It'd need some cooperation from heap_tuple_needs_freeze in
order to work at all, for one thing.

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


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