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Re: High Performance/High Reliability File system on SuSE64

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Christopher Weimann <cweimann(at)k12hq(dot)com>
Cc: "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com>,Andrew Sullivan <ajs(at)crankycanuck(dot)ca>,pgsql-performance(at)postgresql(dot)org
Subject: Re: High Performance/High Reliability File system on SuSE64
Date: 2004-01-31 05:07:53
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-adminpgsql-performance
Christopher Weimann <cweimann(at)k12hq(dot)com> writes:
> You can do snapshots in FreeBSD 5.x with UFS2 as well but that (
> nor XFS snapshots ) will let you backup with the database server
> running.  Just because you will get the file exactly as it was at
> a particular instant does not mean that the postmaster did not
> still have some some data that was not flushed to disk yet.

It *will* work, if you have an instantaneous filesystem snapshot
covering the entire $PGDATA directory tree (both data files and WAL).
Restarting the postmaster on the backup will result in a WAL replay
sequence, and at the end the data files will be consistent.  If this
were not so, we'd not be crash-proof.  The instantaneous snapshot
is exactly equivalent to the on-disk state at the moment of a kernel
crash or power failure, no?

			regards, tom lane

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