Date: Tue, 10 Apr 2007 15:52:00 -0400 From: Tom Lane <tgl@sss.pgh.pa.us> To: Kris Kennaway <kris@obsecurity.org> 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? Message-ID: <555.1176234720@sss.pgh.pa.us> In-Reply-To: <20070410194508.GA73072@xor.obsecurity.org> References: <20070226002234.GA80974@xor.obsecurity.org> <461B69C0.4060707@paradise.net.nz> <25573.1176215022@sss.pgh.pa.us> <20070410184332.GC44123@xor.obsecurity.org> <28537.1176230816@sss.pgh.pa.us> <20070410194508.GA73072@xor.obsecurity.org>
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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
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