Re: Scalability in postgres

2009/5/28 Flavio Henrique Araque Gurgel <flavio(at)4linux(dot)com(dot)br>

> ----- "Scott Marlowe" <scott(dot)marlowe(at)gmail(dot)com> escreveu:
> > On Thu, May 28, 2009 at 12:50 PM, Fabrix <fabrixio1(at)gmail(dot)com> wrote:
> > >
> > > HI.
> > >
> > > Someone had some experience of bad performance with postgres in some
> server
> > > with many processors?
>
> I had.
>
> > > but I have experienced problems with another server that has 8 CPUS
> quad
> > > core (32 cores). The second one only gives me about 1.5 of performance
> of
> > > the first one.
>
> I have had problems with 4 CPUS dual core Hyper Threading (16 logical
> CPUS).
>
> > What model CPUs and chipset on the mobo I wonder?
> >
> > > Monitoring (nmon, htop, vmstat) see that everything is fine (memory,
> HD,
> > > eth, etc) except that processors regularly climb to 100%.
> > >
> > > I can see that the processes are waiting for CPU time:
>
> > > Have postgres problems of lock or degradation of performance with many
> > > CPU's?
> > > Any comments?
> >
> > Looks like a context switch storm, which was pretty common on older
> > Xeon CPUs. I imagine with enough pg processes running on enough CPUs
> > it could still be a problem.
>
> I would ask for your kernel version. uname -a please?
>

sure, and thanks for you answer Flavio...

uname -a
Linux SERVIDOR-A 2.6.18-92.el5 #1 SMP Tue Apr 29 13:16:15 EDT 2008 x86_64
x86_64 x86_64 GNU/Linux

cat /etc/redhat-release
Red Hat Enterprise Linux Server release 5.2 (Tikanga)

>
> It was possible to make the context work better with 2.4.24 with kswapd
> patched around here. 1600 connections working fine at this moment.
>

2.4 is very old, or not?

>
> Try to lower your memory requirements too. Linux kernel needs some space to
> page and scale up. Install some more memory otherwise.
>

how much?
already I have a lot of memory installed in the server 128GB.

> Flavio
>
>