From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Kris Kennaway <kris(at)obsecurity(dot)org> |
Cc: | Mark Kirkwood <markir(at)paradise(dot)net(dot)nz>, current(at)FreeBSD(dot)org, performance(at)FreeBSD(dot)org, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Anyone interested in improving postgresql scaling? |
Date: | 2007-04-10 22:26:37 |
Message-ID: | 4307.1176243997@sss.pgh.pa.us |
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Lists: | pgsql-hackers |
Kris Kennaway <kris(at)obsecurity(dot)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.
> 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.
Sorry, I'm not much of a BSD kernel hacker ... but sleepq_broadcast
seems a rather generic name. Is that called *only* from semop?
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 ...
regards, tom lane
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