From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
cc: Bruce Momjian <bruce@momjian.us>, Andres Freund <andres@2ndquadrant.com>,
 PostgreSQL Bugs <pgsql-bugs@postgresql.org>
Subject: Re: pg_upgrade < 9.3 -> >=9.3 misses a step around multixacts
In-reply-to: <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>
 <20140620173351.GV18688@eldon.alvh.no-ip.org>
Comments: In-reply-to Alvaro Herrera <alvherre@2ndquadrant.com>
 message dated "Fri, 20 Jun 2014 13:33:52 -0400"
Date: Fri, 20 Jun 2014 13:41:42 -0400
Message-ID: <8519.1403286102@sss.pgh.pa.us>
Precedence: bulk
Sender: pgsql-bugs-owner@postgresql.org

Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> Bruce Momjian wrote:
>> 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.

Yeah.  In my mind, at least, there's been a TODO for some time for
pg_resetxlog to make sure that pg_clog and the other SLRU-like files
get populated appropriately when you tell it to change those counters.
You have to have a segment file at the right place or startup fails.

I'm not sure why Alvaro chose to fix this only for pg_multixact, but
fixing that case is better than not fixing anything.

			regards, tom lane


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