Re: understanding postgres issues/bottlenecks

Find !

Dell CERC SATA RAID 2 PCI SATA 6ch

Running lspci -v:

03:09.0 RAID bus controller: Adaptec AAC-RAID (rev 01)
Subsystem: Dell CERC SATA RAID 2 PCI SATA 6ch (DellCorsair)
Flags: bus master, 66MHz, slow devsel, latency 32, IRQ 209
Memory at f8000000 (32-bit, prefetchable) [size=64M]
Expansion ROM at fe800000 [disabled] [size=32K]
Capabilities: [80] Power Management version 2

Any consideration looking at iostat output ?

Cheers and thanks to all!

ste

On Wed, Jan 7, 2009 at 10:31 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.
>