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