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Re: [GENERAL] large object does not exist afterpg_migrator

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Bruce Momjian <bruce(at)momjian(dot)us>
Cc: Jamie Fox <jfox(at)directcommerce(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgreSQL(dot)org>
Subject: Re: [GENERAL] large object does not exist afterpg_migrator
Date: 2009-07-14 00:28:58
Message-ID: 20090714002858.GR4930@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-hackers
Bruce Momjian wrote:
> Alvaro Herrera wrote:
> > Bruce Momjian wrote:
> > > Jamie Fox wrote:
> > 
> > > > I can also see that the pg_largeobject table is different, in the pg_restore
> > > > version the Rows (estimated) is 316286 and Rows (counted) is the same, in
> > > > the pg_migrator version the Rows (counted) is only 180507.
> > 
> > > Wow, I didn't test large objects specifically, and I am confused why
> > > there would be a count discrepancy. I will need to do some research
> > > unless someone else can guess about the cause.
> > 
> > Maybe pg_largeobject is not getting frozen?
> 
> That would explain the change in count, but I thought we froze
> _everything_, and had to.

After a quick chat with Bruce it was determined that we don't freeze
anything (it would be horrid for downtime if we did so in pg_migrator;
and it would be useless if ran anywhere else).  What we do is migrate
pg_clog from the old cluster to the new.  So never mind that hypothesis.

Bruce noticed that the pg_dump/pg_migrator combo is failing to restore
pg_largeobject's relfrozenxid.  We're not sure how this is causing the
errors Jamie is seeing, because what I think should happen is that scans
of the table should fail with failures to open pg_clog files
such-and-such, but not missing tuples ...

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.

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