Re: understanding postgres issues/bottlenecks

If you're stuck with a Dell, the Adaptec 5 series works, I'm using 5085's in a pair and get 1200 MB/sec streaming reads best case with 20 SATA drives in RAID 10 (2 sets of 10, software raid 0 on top). Of course, Dell doesn't like you putting in somebody else's RAID card, but they support the rest of the system when you add in a third party PCIe card.
Sure, they are a bit pricey, but they are also very good performers with drivers for a lot of stuff, including OpenSolaris. I tested a PERC 6 versus this with the same drives, but only 10 total. The Adaptec was 70% faster out of the box, and still 35% faster after tuning the linux OS read-ahead and other parameters.

PERC 5 / 6 cards are LSI re-badged MegaRaid cards, for those interested. With special firmware modifications that make them 'interesting'.

On 1/7/09 1:31 PM, "Scott Marlowe" <scott(dot)marlowe(at)gmail(dot)com> wrote:

On Wed, Jan 7, 2009 at 2:02 PM, Stefano Nichele
<stefano(dot)nichele(at)gmail(dot)com> wrote:
>
> On Tue, Jan 6, 2009 at 7:45 PM, Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>
> wrote:
>>
>> I concur with Merlin you're I/O bound.
>>
>> Adding to his post, what RAID controller are you running, does it have
>> cache, does the cache have battery backup, is the cache set to write
>> back or write through?
>
>
> At the moment I don't have such information. It's a "standard" RAID
> controller coming with a DELL server. Is there any information I can have
> asking to the SO ?

You can run lshw to see what flavor controller it is. Dell RAID
controllers are pretty much either total crap, or mediocre at best.
The latest one, the Perc 6 series are squarely in the same performance
realm as a 4 or 5 year old LSI megaraid. The perc 5 series and before
are total performance dogs. The really bad news is that you can't
generally plug in a real RAID controller on a Dell. We put an Areca
168-LP PCI-x8 in one of our 1950s and it wouldn't even turn on, got a
CPU Error.

Dells are fine for web servers and such. For database servers they're
a total loss. The best you can do with one is to put a generic SCSI
card in it and connect to an external array with its own controller.

We have a perc6e and a perc5e in two different servers, and no matter
how we configure them, we can't get even 1/10th the performance of an
Areca controller with the same number of drives on another machine of
the same basic class as the 1950s.

>> Also, what do you get for this (need contrib module pgbench installed)
>>
>> pgbench -i -s 100
>> pgbench -c 50 -n 10000
>>
>> ? Specifically transactions per second?
>
> I'll run pgbench in the next days.

Cool. That pgbench is a "best case scenario" benchmark. Lots of
small transactions on a db that should fit into memory. If you can't
pull off a decent number there (at least a few hundred tps) then can't
expect better performance from real world usage.

Oh, and that should be:

pgbench -c 50 -t 10000

not -n... not enough sleep I guess.

--
Sent via pgsql-performance mailing list (pgsql-performance(at)postgresql(dot)org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-performance