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

On Tue, Apr 10, 2007 at 03:52:00PM -0400, Tom Lane wrote:
Kris Kennaway <kris@xxxxxxxxxxxxxx> 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 ...

As we've discussed before, by far the bigger issue with postgresql
performance on FreeBSD is the default setting of
update_process_titles=on.

Kris

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