Date: Tue, 10 Apr 2007 18:28:31 -0400 From: Kris Kennaway <kris@obsecurity.org> To: Tom Lane <tgl@sss.pgh.pa.us> Cc: pgsql-hackers <pgsql-hackers@postgresql.org>, performance@FreeBSD.org, current@FreeBSD.org, Mark Kirkwood <markir@paradise.net.nz>, Kris Kennaway <kris@obsecurity.org> Subject: Re: [HACKERS] Anyone interested in improving postgresql scaling? Message-ID: <20070410222831.GA75767@xor.obsecurity.org> In-Reply-To: <4307.1176243997@sss.pgh.pa.us> References: <20070226002234.GA80974@xor.obsecurity.org> <461B69C0.4060707@paradise.net.nz> <20070410184304.GB44123@xor.obsecurity.org> <3721.1176240977@sss.pgh.pa.us> <20070410220923.GA74088@xor.obsecurity.org> <4307.1176243997@sss.pgh.pa.us>
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--LZvS9be/3tNcYl/X Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Apr 10, 2007 at 06:26:37PM -0400, Tom Lane wrote: > Kris Kennaway <kris@obsecurity.org> writes: > > On Tue, Apr 10, 2007 at 05:36:17PM -0400, Tom Lane wrote: > >> Anyway I'd be interested to know what the test case is, and which PG > >> version you were testing. >=20 > > I used 8.2 (and some older version when I first noticed it a year ago) > > and either sysbench or supersmack will show it - presumably anything > > that makes simultaneous queries. Just instrument sleepq_broadcast() > > to e.g. log a KTR event when it wakes more than 1 process and you'll > > see it happening. >=20 > Sorry, I'm not much of a BSD kernel hacker ... but sleepq_broadcast > seems a rather generic name. Is that called *only* from semop? It's part of how wakeup() is implemented. > I'm wondering if you are seeing simultaneous wakeup from some other > cause --- sleep timeout being the obvious possibility. We are aware > of behaviors (search the PG lists for "context swap storm") where a > number of backends will all fail to get a spinlock and do short usleep > or select-timeout waits. In this situation they'd all wake up at the > next scheduler clock tick ... Nope, it's not this. Kris --LZvS9be/3tNcYl/X Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (FreeBSD) iD8DBQFGHA+PWry0BWjoQKURAo2KAKCc7vY5gceTDKOIVm7/jjLD6PrWVwCg6XrM fEXzN+sfe/MtkOx61CjEG9g= =RBAk -----END PGP SIGNATURE----- --LZvS9be/3tNcYl/X--
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