On 09/03/12, Merlin Moncure (mmoncure@xxxxxxxxx) wrote: > On Fri, Mar 9, 2012 at 5:15 AM, Rory Campbell-Lange > <rory@xxxxxxxxxxxxxxxxxx> wrote: > > I've taken the liberty of reposting this message as my addendum to a > > long thread that I started on the subject of adding a new db server to > > our existing 4-year old workhorse got lost in discussion. > > > > Our workload is several small databases totalling less than 40GB of disk > > space. The proposed system has 48GB RAM, 2 * quad core E5620 @ 2.40GHz > > and 4 WD Raptors behind an LSI SAS card. Our supplier has just run a set > > of tests on the machine we intend to buy. The test rig had the following > > setup: > > > > LSI MegaRAID SAS 9260-8i > > Firmware: 12.12.0-0090 > > Kernel: 2.6.39.4 > > Hard disks: 4x WD6000BLHX > > Test done on 256GB volume > > BS = blocksize in bytes > > > > The test tool is fio. I'd be grateful to know if the results below are > > considered acceptable. An ancillary question is whether a 4096 block > > size is a good idea. I suppose we will be using XFS which I understand > > has a default block size of 4096 bytes. > > > > RAID 10 > > -------------------------------------- ... > > -------------------------------------- > > Random write > > > > BS MB/s IOPs > > 512 0000.53 001103.60 > > 1024 0001.15 001179.20 > > 4096 0004.43 001135.30 > > 16384 0017.61 001127.56 > > 65536 0061.39 000982.39 > > 131072 0079.27 000634.16 > > -------------------------------------- > > since your RAM is larger than the database size, read performance is > essentially a non-issue. your major gating factors are going to be > cpu bound queries and random writes -- 1000 IOPS essentially puts an > upper bound on your write TPS, especially if your writes are frequent > and randomly distributed, the case that is more or less simulated by > pgbench with large scaling factors. > > Now, 1000 write tps is quite alot (3.6 mil transactions/hour) and > your workload will drive the hardware consideration. Thanks for your comments, Merlin. With regard to the "gating factors" I believe the following is pertinent: CPU My current server has 2 * quad Xeon E5420 @ 2.50GHz. The server occasionally reaches 20% sutained utilisation according to sar. This cpu has a "passmark" of 7,730. http://www.cpubenchmark.net/cpu_lookup.php?cpu=[Dual+CPU]+Intel+Xeon+E5420+%40+2.50GHz My proposed CPU is an E5620 @ 2.40GHz with CPU "passmark" of 9,620 http://www.cpubenchmark.net/cpu_lookup.php?cpu=[Dual+CPU]+Intel+Xeon+E5620+%40+2.40GHz Since the workload will be very similar I'm hoping for about 20% better CPU performance from the new server, which should drop max CPU load by 5% or so. Random Writes I'll have to test this. My current server (R10 4*15K SCSI) produced the following pgbench stats while running its normal workload: -c -t TPS 5 20000 446 10 10000 542 20 5000 601 30 3333 647 I'd be grateful to know what parameters I should use for a "large scaling factor" pgbench test. Many thanks Rory -- Rory Campbell-Lange rory@xxxxxxxxxxxxxxxxxx Campbell-Lange Workshop www.campbell-lange.net 0207 6311 555 3 Tottenham Street London W1T 2AF Registered in England No. 04551928 -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
