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Re: URGENT: Out of disk space pg_xlog

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, Jeremy Haile <jhaile(at)fastmail(dot)fm>, pgsql-performance(at)postgresql(dot)org
Subject: Re: URGENT: Out of disk space pg_xlog
Date: 2006-12-22 22:15:49
Message-ID: 200612222215.kBMMFnB00280@momjian.us (view raw or flat)
Thread:
Lists: pgsql-performance
Tom Lane wrote:
> "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov> writes:
> > As I understand it, the log space accumulates for the oldest transaction
> > which is still running, and all transactions which started after it.
> 
> No, pg_xlog can be truncated as soon as a checkpoint occurs.  If Jeremy
> wasn't using archive_command then the only possible explanation for
> bloated pg_xlog is that checkpoints were failing.  Which is not unlikely
> if the *data* partition runs out of space.  Were there gripes in the log
> before the system crash?  The scenario we've seen in the past is
> 
> * data partition out of space, so writes fail
> * each time Postgres attempts a checkpoint, writes fail, so the
>   checkpoint fails.  No data loss at this point, the dirty buffers
>   just stay in memory.
> * pg_xlog bloats because we can't truncate away old segments
> * eventually pg_xlog runs out of space, at which point we PANIC
>   and can't continue running the database
> 
> Once you free some space on the data partition and restart, you should
> be good to go --- there will be no loss of committed transactions, since
> all the operations are in pg_xlog.  Might take a little while to replay
> all that log though :-(

Amazing that all works.  What I did not see is confirmation from the
user that the data directory filled up _before_ pg_xlog filled up.

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

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

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