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List:       postgresql-general
Subject:    Re: [HACKERS] 10RC1 crash testing MultiXact oddity
From:       Alvaro Herrera <alvherre () alvh ! no-ip ! org>
Date:       2017-09-30 19:08:45
Message-ID: 20170930190845.hcg3jpeezyyi7ato () alvherre ! pgsql
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Jeff Janes wrote:
> On Fri, Sep 22, 2017 at 1:19 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> 
> > On Fri, Sep 22, 2017 at 3:39 PM, Jeff Janes <jeff.janes@gmail.com> wrote:
> > > It turns out it is not new in pg10.  I spotted in the log file only by
> > > accident while looking for something else.  Now that I am looking for
> > it, I
> > > do see it in 9.6 as well.
> >
> > So I guess the next question is whether it also shows up if you initdb
> > with 9.4.latest and then run the same test.
> >
> 
> git bisect shows that it shows up in 9.5, at this commit:
> 
> commit bd7c348d83a4576163b635010e49dbcac7126f01
> Author: Andres Freund <andres@anarazel.de>
> Date:   Sat Sep 26 19:04:25 2015 +0200
> 
>     Rework the way multixact truncations work.

Oh man.  And I thought we were done with that stuff :-(

> Not really sure what the next step is here.  I could promote the
> ereport(LOG...) to a PANIC to get a core dump, but I don't think that would
> help because presumably the problem occurred early, when the truncation was
> done, not when it was detected.

Probably the best way to track it down is to add some instrumentation
elog(LOG) to the multixact truncation mechanism.

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


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