Re: postgresql and smp linux kernel

zhicheng wang <wang_zc@yahoo.co.uk> wrote:
> Thanks for the clear answer.
>
> What about hyper-threading? At the moment, I have
> hyper-threading enabled and the OS sees four CPUs (two
> physical and two virtual). Do these two virtual ones
> really work as the real ones?

This question really belongs on the list for the OS you're using.  It's
much more dependent on the OS than PostgreSQL.

However, if you're using FreeBSD 5, I can say from experience that
PostgreSQL makes full use of hyperthreaded processors when running on
FreeBSD 5.

If you're not running FreeBSD 5, someone else will have to answer.

> I am asking these because we use SAN disks and the
> secure-path (a fail safe mechanism) only support UP
> kernel. I have to choose do we run smp or do we make
> use of secure-path.
>
> Regards
> cheng
>
>
>
>  --- Bill Moran <wmoran@potentialtech.com> wrote:
> > zhicheng wang <wang_zc@yahoo.co.uk> wrote:
> >
> > > Thanks Oliver Elphick
> > > does this mean that the applications do not need
> > to be
> > > multi-threading in order to use multi-processors?
> >
> > Yes, that's what it means.  Although you've probably
> > oversimplified it
> > too much.  Multi-process applications make use of
> > multiple processors
> > just as well as multi-threaded apps do.
> >
> > >  --- Oliver Elphick <olly@lfix.co.uk> wrote:
> > > > On Mon, 2004-08-09 at 11:10, zhicheng wang
> > wrote:
> > > > > Dear all
> > > > >
> > > > > i have a dedicated server mainly running
> > > > postgresql,
> > > > > currently rh-posgtresql-7.3.6.7 (and samba,
> > ypbind
> > > > > etc). The server is a dual processor machine
> > and
> > > > the
> > > > > OS is RHEL AS 3.
> > > > >
> > > > > I am currently running
> > > > kernel-smp-2.4.21-15.0.4.EL.
> > > > >
> > > > > My question is: do i need to run smp kernel
> > for
> > > > > postgresql? What is benefit of it? If I run UP
> > > > kernel,
> > > > > what do I lose from the point view of PG?
> > > >
> > > > You do not NEED it for Pg, but it will improve
> > > > performance.  Each
> > > > separate session gets a different process and
> > > > therefore has a change to
> > > > run on the second processor concurrently with
> > > > another session on the
> > > > first processor.  The same goes for any other
> > > > processes that are
> > > > running, of course.
> > > >
> > > > If you do not use an SMP kernel, one of your
> > > > processors will sit there
> > > > for ever doing nothing, which is money down the
> > > > drain.
> > > >
> > > > --
> > > > Oliver Elphick
> >
> > > >    olly@lfix.co.uk
> > > > Isle of Wight
> > > > http://www.lfix.co.uk/oliver
> > > > GPG: 1024D/A54310EA  92C8 39E7 280E 3631 3F0E
> > 1EC0
> > > > 5664 7A2F A543 10EA
> > > >
> > > > ========================================
> > > >      "Be still before the LORD and wait
> > patiently
> > > > for him;
> > > >       do not fret when men succeed in their
> > ways,
> > > > when they
> > > >       carry out their wicked schemes."
> > > >                             Psalms 37:7
> > > >
> > > >
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> > > >
> > > > http://www.postgresql.org/docs/faqs/FAQ.html
> > > >
> > > >
> > >
> > > =====
> > > Best wishes
> > > Z C Wang
> > >
> > >
> > >
> > >
> > >
> > >
> >
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> > Potential Technologies
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> =====
> Best wishes
> Z C Wang
>
>
>
>
>
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--
Bill Moran
Potential Technologies
http://www.potentialtech.com