From: Bruce Momjian <bruce@momjian.us>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: Andres Freund <andres@2ndquadrant.com>
Cc: PostgreSQL Bugs <pgsql-bugs@postgresql.org>
Subject: Re: pg_upgrade < 9.3 -> >=9.3 misses a step around multixacts
Date: Wed, 18 Jun 2014 22:06:33 -0400
Message-ID: <20140619020633.GA20469@momjian.us> (raw)
In-Reply-To: <20140619015205.GD3806@momjian.us>
References: <20140530121631.GE25431@alap3.anarazel.de>
<20140530132916.GM28490@momjian.us>
<20140618225131.GN18688@eldon.alvh.no-ip.org>
<20140619015205.GD3806@momjian.us>
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On Wed, Jun 18, 2014 at 09:52:05PM -0400, Bruce Momjian wrote:
> On Wed, Jun 18, 2014 at 06:51:31PM -0400, Alvaro Herrera wrote:
> > > This is a bug in 9.3 pg_upgrade as well? Why has no one reported it
> > > before?
> >
> > I think one reason is that not all upgrades see an issue here; for old
> > clusters that haven't gone beyond the 0000 offset file, there is no
> > problem. For clusters that have gone beyond 0000 but not by much, the
> > file will be deleted during the first truncation. It only becomes a
> > problem if the cluster is close enough to 2^31. Another thing to keep
> > in consideration is that initdb initializes all databases' datminmxid to
> > 1. If the old cluster was past the 2^31 point, it means the datminmxid
> > doesn't move from 1 until the actual wraparound.
>
> OK, so the xid has to be beyond 2^31 during pg_upgrade to trigger a
> problem? That might explain the rare reporting of this bug. What would
> the test query look like so we can tell people when to remove the '0000'
> files? Would we need to see the existence of '0000' and high-numbered
> files? How high? What does a 2^31 file look like?
Also, what would a legitimate 0000 file at wrap-around time look like?
Would there have to be an 'ffff' or 'ffffff' file?
--
Bruce Momjian <bruce@momjian.us> http://momjian.us
EnterpriseDB http://enterprisedb.com
+ Everyone has their own god. +
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To: pgsql-bugs@postgresql.org
Cc: bruce@momjian.us, alvherre@2ndquadrant.com, andres@2ndquadrant.com
Subject: Re: pg_upgrade < 9.3 -> >=9.3 misses a step around multixacts
In-Reply-To: <20140619020633.GA20469@momjian.us>
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