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Re: archived WALL files question

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Frederiko Costa" <frederiko(at)gmail(dot)com>
Cc: <pgsql-admin(at)postgresql(dot)org>
Subject: Re: archived WALL files question
Date: 2010-04-19 18:41:43
Message-ID: 4BCC5D970200002500030A80@gw.wicourts.gov (view raw or flat)
Thread:
Lists: pgsql-admin
Frederiko Costa <frederiko(at)gmail(dot)com> wrote:
 
> log files are being copied directly to the /mnt/data dir.
> However, the same segments are not in the pg_xlog 
> dir. Is this a default behaviour?
 
Yes, the pg_xlog directory tries to keep a set of files ready to
receive WAL, and to hold it until the next checkpoint completes,
while the archive directory holds WAL files which have filled or
reached the archive_timeout limit.  There can be some overlap, but
basically you can view the archive as "past" and pg_xlog as
"future", with some potential overlap in "the present".
 
> Must I set archive_timeout?
 
No, but once a database write occurs, you don't have it backed up
until the WAL file is written to the archive directory. 
archive_timeout is for those who want some wall-clock bounds on how
much they can lose in, say, a drive failure.  If the database can be
reloaded from some other source, or the data has no real value, it
may not pay to use this feature.
 
-Kevin

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