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.
> 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