From: Andres Freund <andres@2ndquadrant.com>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Bruce Momjian <bruce@momjian.us>
Cc: Stephen Frost <sfrost@snowman.net>
Cc: pgsql-hackers@postgresql.org
Subject: Re: MultiXactId error after upgrade to 9.3.4
Date: Wed, 23 Apr 2014 23:34:27 +0200
Message-ID: <20140423213427.GA12442@awork2.anarazel.de> (raw)
In-Reply-To: <20140423193005.GS25695@eldon.alvh.no-ip.org>
References: <20140330185349.GD4582@tamriel.snowman.net>
<20140331115452.GT9567@eldon.alvh.no-ip.org>
<20140331115713.GA18358@alap3.anarazel.de>
<20140423180102.GP25695@eldon.alvh.no-ip.org>
<20140423182804.GA21458@momjian.us>
<20140423184214.GQ25695@eldon.alvh.no-ip.org>
<20140423184716.GA22722@momjian.us>
<20140423185120.GR25695@eldon.alvh.no-ip.org>
<60097392-07aa-4310-8632-43b7b09c1822@email.android.com>
<20140423193005.GS25695@eldon.alvh.no-ip.org>
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On 2014-04-23 16:30:05 -0300, Alvaro Herrera wrote:
> 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.
I think if you want to add something like this it should be added
*inside* the if (MultiXactIdPrecedes(multi, cutoff_multi)) block in
FreezeMultiXactId(). There it seems to make quite a bit of sense.
Greetings,
Andres Freund
--
Andres Freund http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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To: pgsql-hackers@postgresql.org
Cc: andres@2ndquadrant.com, alvherre@2ndquadrant.com, bruce@momjian.us, sfrost@snowman.net
Subject: Re: MultiXactId error after upgrade to 9.3.4
In-Reply-To: <20140423213427.GA12442@awork2.anarazel.de>
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