From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alvaro Herrera <alvherre@commandprompt.com>
Cc: Greg Stark <gsstark@mit.edu>
Cc: Pierre C <lists@peufeu.com>
Cc: Greg Smith <greg@2ndquadrant.com>
Cc: Dave Crooke <dcrooke@gmail.com>
Cc: Paul McGarry <paul@paulmcgarry.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: shared_buffers advice
Date: Tue, 16 Mar 2010 17:58:34 -0400
Message-ID: <15417.1268776714@sss.pgh.pa.us> (raw)
In-Reply-To: <20100316214903.GH3037@alvh.no-ip.org>
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Alvaro Herrera <alvherre@commandprompt.com> writes:
> Tom Lane escribió:
>> Reorder to what, though? You still have the problem that we don't know
>> much about the physical layout on-disk.
> Well, to block numbers as a first step.
fsync is a file-based operation, and we know exactly zip about the
relative positions of different files on the disk.
> However, this reminds me that sometimes we take the block-at-a-time
> extension policy too seriously.
Yeah, that's a huge performance penalty in some circumstances.
> We had a customer that had a
> performance problem because they were inserting lots of data to TOAST
> tables, causing very frequent extensions. I kept wondering whether an
> allocation policy that allocated several new blocks at a time could be
> useful (but I didn't try it). This would also alleviate fragmentation,
> thus helping the physical layout be more similar to logical block
> numbers.
That's not going to do anything towards reducing the actual I/O volume.
Although I suppose it might be useful if it just cuts the number of
seeks.
regards, tom lane
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To: pgsql-performance@postgresql.org
Cc: tgl@sss.pgh.pa.us, alvherre@commandprompt.com, gsstark@mit.edu, lists@peufeu.com, greg@2ndquadrant.com, dcrooke@gmail.com, paul@paulmcgarry.com
Subject: Re: shared_buffers advice
In-Reply-To: <15417.1268776714@sss.pgh.pa.us>
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