From: Tom Lane <tgl@sss.pgh.pa.us>
To: Bill Moran <wmoran@collaborativefusion.com>
Cc: Jim Nasby <decibel@decibel.org>
Cc: Postgresql list Performance <pgsql-performance@postgresql.org>
Subject: Re: Fragmentation of WAL files
Date: Thu, 26 Apr 2007 11:37:42 -0400
Message-ID: <24354.1177601862@sss.pgh.pa.us> (raw)
In-Reply-To: <20070426080050.522ef7b5.wmoran@collaborativefusion.com>
References: <3BD44C5D-E402-43EB-8FFD-1A4BC97AFD0C@decibel.org>
<20070426080050.522ef7b5.wmoran@collaborativefusion.com>
> In response to Jim Nasby <decibel@decibel.org>:
>> I was recently running defrag on my windows/parallels VM and noticed
>> a bunch of WAL files that defrag couldn't take care of, presumably
>> because the database was running. What's disturbing to me is that
>> these files all had ~2000 fragments.
It sounds like that filesystem is too stupid to coalesce successive
write() calls into one allocation fragment :-(. I agree with the
comments that this might not be important, but you could experiment
to see --- try increasing the size of "zbuffer" in XLogFileInit to
maybe 16*XLOG_BLCKSZ, re-initdb, and see if performance improves.
The suggestion to use ftruncate is so full of holes that I won't
bother to point them all out, but certainly we could write more than
just XLOG_BLCKSZ at a time while preparing the file.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, wmoran@collaborativefusion.com, decibel@decibel.org
Subject: Re: Fragmentation of WAL files
In-Reply-To: <24354.1177601862@sss.pgh.pa.us>
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