Re: [HACKERS] Anyone interested in improving postgresql scaling?

From: Tom Lane <tgl_at_sss.pgh.pa.us>
Date: Tue, 10 Apr 2007 18:26:37 -0400
Kris Kennaway <kris_at_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.

> 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
Received on Tue Apr 10 2007 - 20:26:38 UTC

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