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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 14:43:04 -0400"
Date: Tue, 10 Apr 2007 17:36:17 -0400
Message-ID: <3721.1176240977@sss.pgh.pa.us>
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:
> I have not studied the exact code path, but there are indeed multiple
> wakeups happening from the semaphore code (as many as the number of
> active postgresql processes).  It is easy to instrument
> sleepq_broadcast() and log them when they happen.

There are certainly cases where Postgres will wake up a number of
processes in quick succession, but that should happen from a separate
semop() kernel call, on a different semaphore, for each such process.
If there's really multiple processes being released by the same semop()
then there's a bug we need to look into (or maybe it's a kernel bug?).
Anyway I'd be interested to know what the test case is, and which PG
version you were testing.

			regards, tom lane