Re: [mux@FreeBSD.org: Re: Anyone interested in improving postgresql scaling?]

Maxime Henrion <mux(at)freebsd(dot)org> writes:
> Thanks for forwarding my mail, Kris! To Tom: if you can get my mails
> to reach pgsql-hackers@ somehow that would be just great :-).

They'll get approved eventually, just like mine to the BSD lists will
get approved eventually ;-)

>> The only thing we could do to fix that from our end would be to use
>> a smaller sema-set size on *BSD platforms. Is the overhead per sema set
>> small enough to make this a sane thing to do? Will we be likely to
>> run into system limits on the number of sets?

> I'm not familiar enough with the PostgreSQL code to know what impact
> such a change could have, but since the problem is clearly on our
> side here, I would advise against doing changes in PostgreSQL that
> are likely to complicate the code for little gain. We still didn't
> even fully measure how much the useless wakups cost us since we're
> running into other contention problems with my patch that removes
> those. And, as you point out, there are complications ensuing with
> respect to system limits (we already ask users to bump them when
> they install PostgreSQL).

OK, it was just an off-the-cuff idea.

> I think the high number of setproctitle() calls are more problematic
> to us at the moment, Kris can comment on that.

As of PG 8.2 it is possible to turn those off. I don't think there's a
lot of enthusiasm for turning them off by default ... at least not yet.
But it might make sense to point out in the PG documentation that
update_process_title is particularly costly on platforms X, Y, and Z.
Do you know if this issue affects all the BSDen equally?

regards, tom lane