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Re: Advice sought : new database server

From: Craig James <cjames(at)emolecules(dot)com>
To: Rory Campbell-Lange <rory(at)campbell-lange(dot)net>
Cc: Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Advice sought : new database server
Date: 2012-03-05 16:56:08
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Lists: pgsql-performance
On Sun, Mar 4, 2012 at 10:36 AM, Rory Campbell-Lange <
rory(at)campbell-lange(dot)net> wrote:

> We do have complex transactions, but I haven't benchmarked the
> performance so I can't describe it. Few of the databases are at the many
> million row size at the moment, and we are moving to an agressive scheme
> of archiving old data, so we hope to keep things fast.
> However I thought 15k disks were a pre-requisite for a fast database
> system, if one can afford them? I assume if all else is equal the 1880
> controller will run 20-40% faster with 15k disks in a write-heavy
> application. Also I would be grateful to learn if there is a good reason
> not to use 2.5" SATA disks.

Without those benchmarks, you can't really say what "fast" means.  There
are many bottlenecks that will limit your database's performance; the
disk's spinning rate is just one of them.  Memory size, memory bandwidth,
CPU, CPU cache size and speed, the disk I/O bandwidth in and out, the disk
RPM, the presence of a BBU controller ... any of these can be the
bottleneck.  If you focus on the disk's RPM, you may be fixing a bottleneck
that you'll never reach.

We 12 inexpensive 7K SATA drives with an LSI/3Ware 9650SE and a BBU, and
have been very impressed by the performance.  8 drives in RAID10, two in
RAID1 for the WAL, one for Linux and one spare.  This is on an 8-core
system with 12 GB memory:

pgbench -i -s 100 -U test
pgbench -U test -c ... -t ...

-c  -t     TPS
5   20000  3777
10  10000  2622
20  5000   3759
30  3333   5712
40  2500   5953
50  2000   6141


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