Re: PostgreSQL performance on various distribution stock kernels

On Mon, 2007-11-26 at 17:00 -0600, Scott Marlowe wrote:
> On Nov 26, 2007 4:50 PM, Damon Hart <dhcom(at)sundial(dot)com> wrote:
> >
> > So, what's different between these tests? I'm seeing performance
> > differences of between +65% to +90% transactions per second of the
> > OpenVZ kernel running on the HN over the stock Fedora 8 kernel. Is
> > this reflective of different emphasis between RHEL and Fedora kernel
> > builds? Some OpenVZ optimization on top of the RHEL5 build? Something
> > else? Where should I look?
> >
> > any insights much appreciated,
>
> How many TPS are you seeing on each one? If you are running 10krpm
> drives and seeing more than 166.66 transactions per second, then your
> drives are likely lying to you and not actually fsyncing, and it could
> be that fsync() on IDE / SATA has been implemented in later kernels
> and it isn't lying.
>
> Hard to say for sure.
>
> What does vmstat 1 have to say on each system when it's under load?

I will have to repeat the tests to give you any vmstat info, but perhaps
a little more raw input might be useful.

Test H/W:

Dell Precision 650 Dual
Intel CPU: Dual XEON 2.4GHz 512k Cache
RAM: 4GB of DDR ECC
Hard Drive: 4 x 36GB 10K 68Pin SCSI Hard Drive

pgbench
scale: 50
clients: 50
transactions per client: 100

stats for 30 runs each kernel in TPS (excluding connections
establishing)

OpenVZ (RHEL5 derived 2.6.18 series)

average: 446
maximum: 593
minimum: 95
stdev: 151
median: 507

stock Fedora 8 (2.6.23 series)

average: 270
maximum: 526
minimum: 83
stdev: 112
median: 268

Does your 10K RPM drive 166 TPS ceiling apply in this arrangement with
multiple disks (the PostgreSQL volume spans three drives, segregated
from the OS) and multiple pgbench clients? I'm fuzzy on whether these
factors even enter into that rule of thumb. At least as far as the
PostgreSQL configuration is concerned, fsync has not been changed from
the default.

Damon