Re: shared_buffers > 284263 on OS X

Am 19.11.2006 um 04:13 schrieb Brian Wipf:

> It certainly is unfortunate if Guido's right and this is an upper
> limit for OS X. The performance benefit of having high
> shared_buffers on our mostly read database is remarkable.

I hate to say that, but if you want best performance out of
PostgreSQL, Mac OS X (Server) isn't the best OS to achieve this. This
might change in the future (who knows), but currently you get more
out of Linux. Brendan might have some of my old benchmarks. We wrote
a couple of mails about that a couple of months ago.

If you're interested, I can run a pgbench benchmark on my desktop
machine in the company comparing Mac OS X Tiger to Yellow Dog Linux
with 8.1.5 and 8.2beta3. If I remember correctly I have YDL installed
on a second hard drive and should be about a couple of minutes to
install the latest PostgreSQL release.

So, there is no need for you to do the testing of YDL on your Xserves
without knowing pretty much for sure, that it will bring you some
benefit.

As far as I remember I got around 50% to 80% better performance with
Linux on the same machine with same settings but that was in times
when I hardly new anything about optimizing the OS and PostgreSQL for
OLTP performance.

Some hints from what I have learned in the past about PostgreSQL on
Mac OS X / Apple machines:

- Turn off Spotlight on all harddrives on the server (in /etc/
hostconfig)

- Use the latest compilers (gcc) and PostgreSQL versions (I'm sure,
you do ... ;-)).

- If you need the highest possible performance, use Linux instead of
Mac OS X for the DB server. :-/

I know that some of the tips don't help with your current setup.
Perhaps the switch to Linux on the DB machines might help. But I
don't know whether they work good with the XserveRAID you have. Might
bring you some headache - I don't know, perhaps you can find opinions
on the net.

Regarding the memory test I also tried it on Leopard and it seems
that the problem persists. Perhaps someone from Apple can say
something about that. We might ask on the Darwin list.

I'll post some results tomorrow.

cug