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From: Tom Lane <tgl@sss.pgh.pa.us>
To: mark@mark.mielke.cc
Cc: Jim C. Nasby <jnasby@pervasive.com>
Cc: Steve Poe <steve.poe@gmail.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Postgresql Performance on an HP DL385 and
Date: Tue, 15 Aug 2006 16:05:17 -0400
Message-ID: <19783.1155672317@sss.pgh.pa.us> (raw)
In-Reply-To: <20060815183147.GB12834@mark.mielke.cc>
References: <3E37B936B592014B978C4415F90D662D03FFEF6E@MI8NYCMAIL06.Mi8.com>
	<721b21dc0608082245u6ee62e7dg522ff18e4d72683@mail.gmail.com>
	<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>

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).

			regards, tom lane



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