Date: Tue, 15 Aug 2006 16:29:48 -0400
From: mark@mark.mielke.cc
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: "Jim C. Nasby" <jnasby@pervasive.com>, Steve Poe <steve.poe@gmail.com>,
	pgsql-performance@postgresql.org
Subject: Re: Postgresql Performance on an HP DL385 and
Message-ID: <20060815202948.GC13695@mark.mielke.cc>
References: <20060809210539.GR40481@pervasive.com>
	<1155180553.13315.0.camel@amd64-gentoo-laptop>
	<20060810110935.GF2900@mathom.us>
	<20060814153841.GF27928@pervasive.com>
	<721b21dc0608140851v2332cdf9g59808004c983540f@mail.gmail.com>
	<20060814170545.GG27928@pervasive.com>
	<20060814170902.GN2900@mathom.us>
	<20060815162926.GS27928@pervasive.com>
	<20060815183147.GB12834@mark.mielke.cc>
	<19783.1155672317@sss.pgh.pa.us>
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On Tue, Aug 15, 2006 at 04:05:17PM -0400, Tom Lane wrote:
> mark@mark.mielke.cc writes:
> > I've been worrying about this myself, and my current conclusion is that
> > ext2 is bad because: a) fsck, and b) data can be lost or corrupted, which
> > could lead to the need to trash the xlog.
> > Even ext3 in writeback mode allows for the indirect blocks to be updated
> > without the data underneath, allowing for blocks to point to random data,
> > or worse, previous apparently sane data (especially if the data is from
> > a drive only used for xlog - the chance is high that a block might look
> > partially valid?).
> At least for xlog, this worrying is misguided, because we zero and fsync
> a WAL file before we ever put any valuable data into it.  Unless the
> filesystem is lying through its teeth about having done an fsync, there
> should be no metadata changes happening for an active WAL file (other
> than mtime of course).

Hmmm... I may have missed a post about this in the archive.

WAL file is never appended - only re-written?

If so, then I'm wrong, and ext2 is fine. The requirement is that no
file system structures change as a result of any writes that
PostgreSQL does. If no file system structures change, then I take
everything back as uninformed.

Please confirm whichever. :-)

Cheers,
mark

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