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Re: Bug: Unreferenced temp tables disables vacuum to update xid

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>
Cc: Alvaro Herrera <alvherre(at)commandprompt(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Bug: Unreferenced temp tables disables vacuum to update xid
Date: 2008-01-07 16:58:29
Message-ID: 200801071658.m07GwTY04164@momjian.us (view raw or flat)
Thread:
Lists: pgsql-hackers
Joshua D. Drake wrote:
> > >> SELECT oid::regclass FROM pg_class WHERE
> > >> reltoastrelid='pg_toast.pg_toast_49013869'::regclass;
> > >>
> > >> oid | pg_temp_24.tmp_isp_blk_chk
> > >>
> > >> The hack to get this cleaned up was to connect about 2 dozen times
> > >> (to get to slot 24) with psql via different sessions and create
> > >> temp tables. Once we hit slot 24, the probably instantly went away
> > >> and the database returned to normal state.
> > 
> > Ah -- interesting.  This is a known issue, but we haven't found a
> > solution yet.
> > 
> 
> Is there bug number?

I assume it is this TODO item:

        o Prevent long-lived temporary tables from causing frozen-xid
          advancement starvation

          The problem is that autovacuum cannot vacuum them to set frozen xids;
          only the session that created them can do that.
          http://archives.postgresql.org/pgsql-general/2007-06/msg01645.php

but am confused how the fix worked.  Have all of these backends been
active for 1 billion transactions?

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

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

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