Re: Scalability in postgres

[Fabrix <fabrixio1@xxxxxxxxx>]

2009/5/28 Flavio Henrique Araque Gurgel <flavio@xxxxxxxxxxxxx>

----- "Scott Marlowe" <scott.marlowe@xxxxxxxxx> escreveu:

> On Thu, May 28, 2009 at 12:50 PM, Fabrix <fabrixio1@xxxxxxxxx> 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