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

On Tue, Apr 10, 2007 at 06:26:37PM -0400, Tom Lane wrote:
Kris Kennaway <kris@xxxxxxxxxxxxxx> 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?

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

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