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To: Kris Kennaway <kris@obsecurity.org>
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Comments: In-reply-to Kris Kennaway <kris@obsecurity.org>
	message dated "Tue, 10 Apr 2007 15:45:08 -0400"
Date: Tue, 10 Apr 2007 15:52:00 -0400
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From: Tom Lane <tgl@sss.pgh.pa.us>
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Cc: performance@FreeBSD.org, current@FreeBSD.org,
	Mark Kirkwood <markir@paradise.net.nz>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: [HACKERS] Anyone interested in improving postgresql scaling? 
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Kris Kennaway <kris@obsecurity.org> writes:
> On Tue, Apr 10, 2007 at 02:46:56PM -0400, Tom Lane wrote:
>> Oh, I'm sure the BSD kernel acts as you describe.  But Mark's point is
>> that Postgres never has more than one process waiting on any particular
>> SysV semaphore, and so the problem doesn't really affect us.

> To be clear, some behaviour that postgresql does with sysv semaphores
> causes wakeups of many processes at once.  i.e. if you have 20
> clients, you will get up to 20 wakeups.  I haven't studied the precise
> cause of this, but it is empirically true.  This is the scaling
> problem I described, and it's what mux's patch addresses.

[ shrug... ]  To the extent that that happens, it's Postgres' own issue,
and no amount of kernel rejiggering will change it.  But I certainly
have no objection to a patch that fixes the kernel behavior ...

			regards, tom lane