Date: Fri, 20 Jun 2014 13:33:52 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Bruce Momjian <bruce@momjian.us>
Cc: Andres Freund <andres@2ndquadrant.com>,
 PostgreSQL Bugs <pgsql-bugs@postgresql.org>
Subject: Re: pg_upgrade < 9.3 -> >=9.3 misses a step around multixacts
Message-ID: <20140620173351.GV18688@eldon.alvh.no-ip.org>
References: <20140619020633.GA20469@momjian.us>
 <20140619015205.GD3806@momjian.us>
 <20140619014034.GC3806@momjian.us>
 <20140619220425.GQ18688@eldon.alvh.no-ip.org>
 <20140619221240.GC27747@eldon.alvh.no-ip.org>
 <20140620171915.GC29143@momjian.us>
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Bruce Momjian wrote:
> On Thu, Jun 19, 2014 at 06:12:41PM -0400, Alvaro Herrera wrote:
> > BTW I hacked up pg_resetxlog a bit to make it generate the necessary
> > pg_multixact/offset file when -m is given.  This is not acceptable for
> > commit because it duplicates the #defines from pg_multixact.c, but maybe
> > we want this functionality enough that we're interested in a more
> > complete version of this patch; also it unconditionally writes one zero
> > byte to the file, which is of course wrong if the file exists and
> > already contains data.
> 
> Why would we want this if the system functions fine without those files
> being created?  I don't think we want pg_resetxlog to be doing anything
> except changing pg_controldata.

I don't understand why you say the system functions fine.  If you move
the multixactid with pg_resetxlog to a point which doesn't have the
necessary file and page, the system will not start.  Only pg_upgrade
knows to create the file appropriately, but normal operation doesn't.

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


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