Re: Purchasing the correct hardware: dual-core intel? Big cache?

Bill

start with looking the DB design - I;ve had batch runs go from 5 days down
to 1/2 day purely by tuning the SQL. I'm not kidding, all the DB tuning
quides say look at the SQL/design first, then look at hardware like
disk/data layout, then finally the CPU.

There's lots of info about tuning on Postgress, use this, you'll get more
out of the app this way than spending money chucking hardware at it.

--
martin

On 4/25/06, Bill Moran <wmoran@xxxxxxxxxxxxxxxxxxxxxxx> wrote:

On Tue, 25 Apr 2006 13:28:50 +0100
"Martin Hepworth" <maxsec@xxxxxxxxx> wrote:
Bill

if the database is CPU dependant I'd look at tuning the queries/indexes
and
that stuff...it really shouldn't be CPU bound.

That's in progress, and it's going to be an ongoing process as the
application goes through versions.

Fact is, with 4G of RAM most of the data sits in RAM, so reads incur
no or little IO. With high-end SCSI disks in RAID-10 and a battery-
backed cache, burst writes are cached, thus lightening fast, and
we've been unable to run the application hard enough to saturate
the SCSI bus so far.

So ... the current bottleneck is CPU.


--
martin

On 4/24/06, Bill Moran <wmoran@xxxxxxxxxxxxxxxxx> wrote:

On Mon, 24 Apr 2006 23:03:59 +0100
"Martin Hepworth" <maxsec@xxxxxxxxx> wrote:

Bill

depends on the application itself, but more RAM and the disk layout
(RAID)
will be more important than the CPU. Also depends on how write-heavy
the
apps are...

Thanks for the feedback, Martin.

I'm fully aware of the app-dependency - what I'm looking for is a way
to test the application. I've got 3 different clusters available for
testing, but I'm not sure how to tell if the cache is getting used
heavily or not.

I've already determined that the database server is CPU-bound under
our test load. With high-speed SCSI disks and battery-backed RAID,
there's not enough IO to stress the disk subsystem. RAM is almost a
non-issue. With the machine stressed at full load, it's only using
1/8 of the available RAM.

So, my current bottleneck is CPU power. And the boss has asked me
for the best way to overcome this bottleneck. We're looking at either
the same CPUs we already have, but with _huge_ caches (8m) - or going
with more CPUs by getting true dual-core pentiums.

The question this all pivots on is will 8M of cache be a significant
improvement? If not, then we're going with the dual-core CPUs. What
I'd like is some way to take an existing system and determine how
often
the cache is getting invalidated, so I can make some guesstemate as to
whether more cache will help or not.


--
martin

On 4/24/06, Bill Moran <wmoran@xxxxxxxxxxxxxxxxx> wrote:


I've been asked to make some hardware recommendations, I'm hoping
some
folks on the list can make some suggestions.

We're looking hard at getting either Intel dual-core procs, or
getting
hyperthreaded procs with huge (8M) caches.

We currently have a few dual proc Intel HT machines that we can
test
out our workload on, and I'm trying to get a feel for how to
determine
if a larger cache size will generate better performance than
replacing
HT procs with full-blown dual-core procs. We're looking at the
6850
from Dell, which supports both processor families:



http://www1.us.dell.com/content/products/productdetails.aspx/pedge_6850?c=us&cs=555&l=en&s=biz

The goal for these machines is to serve out PosgreSQL databases to
as
many Apache+php front ends as we can hang off each one. So we're
trying
to purchase hardware that will create a DB server that can handle
a
lot
of web server front ends.

I have a Dell 2850 (dual HT procs) here that I can use for
testing.
I'm a little fuzzy on determining how well the cache is working,
so
I'm
stuck on whether or not the 8M cache that's available on the HT
units
is worth the money or not. Can anyone suggest a testing
methodology
that will isolate this particular aspect?

--
Bill Moran
Collaborative Fusion Inc.
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--
Bill Moran
Collaborative Fusion Inc.

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