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Re: [GENERAL] large object does not exist after pg_migrator

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
Cc: Jamie Fox <jfox(at)directcommerce(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgreSQL(dot)org>
Subject: Re: [GENERAL] large object does not exist after pg_migrator
Date: 2009-07-14 03:03:04
Message-ID: 200907140303.n6E334h02217@momjian.us (view raw or flat)
Thread:
Lists: pgsql-generalpgsql-hackers
Alvaro Herrera wrote:
> 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 ...

Jamie, is it possible for you to apply the attached patch to the 8.4
server, install the new pg_dump, and run the test again to see if
pg_largeobject is fixed?  This patch properly sets the relfrozenxid in
the system tables for each database.

-- 
  Bruce Momjian  <bruce(at)momjian(dot)us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + If your life is a hard drive, Christ can be your backup. +

Attachment: /pgpatches/largeobject
Description: text/x-diff (2.4 KB)

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