On Tue, Jun 13, 2006 at 03:55:38PM -0500, Jim Nasby wrote:
>
> On Jun 12, 2006, at 10:38 AM, Kris Kennaway wrote:
> >>>FYI, the biggest source of contention is via semop() - it might be
> >>>possible to optimize that some more in FreeBSD, I don't know.
> >>
> >>Yeah, I've seen PostgreSQL on FreeBSD fall over at high load with
> >>a lot
> >>of procs in either semwait or semlock. :(
> >
> >Part of that is Giant contention again; for example on 6.x semop() and
> >setproctitle() both want to acquire it, so they'll fight with each
> >other and with anything else on the system that wants Giant
> >(e.g. IPv6, or the USB stack, etc). As I mentioned Giant is not an
> >issue here going forward, but there is still as much lock contention
> >just between semop() calls running on different CPUs. It may be
> >possible for someone to implement more fine-grained locking here, but
> >I don't know if there is available interest.
>
> BTW, there's another FBSD performance odditiy I've run across. Running
>
> pg_dump -t email_contrib -COx stats | bzip2 > ec.sql.bz2 &
>
> which dumps the email_contrib table to bzip2 then to disk, the OS
> won't use more than 1 CPU on an SMP system... unless the data is
> cached. According to both gstat and systat -v, the system isn't I/O
> bound; both are reporting the RAID10 with that table on it as only
> about 10% busy. If I let that command run for a bit then cancel it
> and re-start it so that the beginning of that table is in cache, it
> will use one entire CPU for bzip2, which is what I'd expect to happen.
Hmm, odd..maybe something with the scheduler. I'd need access to a
test case to be able to figure it out though.
Kris
