Guillaume Smet a écrit :
Hi all, I'm currently benchmarking the new PostgreSQL server of one of our customers with PostgreSQL 8.3 beta4. I have more or less the same configuration Stefan tested in his blog [1]: - Dell 2900 with two brand new X5365 processors (quad core 3.0 GHz), 16 GB of memory - a RAID1 array for pg_xlog and a 6 disks RAID10 array for data (I moved pg_xlog to the RAID10 array for a few runs - same behaviour) - all 73 GB 15k drives - CentOS 5.1 - 64 bits
Which kernel do you have ?
I started working on pgbench tests. I made a "not so stupid" configuration to begin with and I was quite disappointed by my results compared to Stefan's. I decided to test with a more default shared_buffers configuration to be able to compare my results with Stefan's graph [2]. And the fact is that with a very low shared_buffers configuration, my results are quite similar to Stefan's results but, as soon as I put higher values of shared_buffers, performances begins degrading [3]. I performed my tests with: pgbench -i -s 100 -U postgres bench and pgbench -s 100 -c 100 -t 30000 -U postgres bench. Of course, I initialize the database before each run. I made my tests in one direction then in the other with similar results so it's not a degradation due to consecutive runs. I lowered the number of concurrent clients to 50 because 100 is quite high and I obtain the same sort of results: shared_buffers=32MB: 1869 tps shared_buffers=64MB: 1844 tps shared_buffers=512MB: 1676 tps shared_buffers=1024MB: 1559 tps Non default parameters are: max_connections = 200 work_mem = 32MB wal_buffers = 1024kB checkpoint_segments = 192 effective_cache_size = 5GB (I use more or less the configuration used by Stefan - I had the same behaviour with default wal_buffers and checkpoint_segments) While monitoring the server with vmstat, I can't see any real reason why it's slower. When shared_buffers has a higher value, I/O are lower, context switches too and finally performances. The CPU usage is quite similar (~50-60%). I/O doesn't limit the performances AFAICS. I must admit I'm a bit puzzled. Does anyone have any pointer which could explain this behaviour or any way to track the issue? I'll be glad to perform any test needed to understand the problem. Thanks. [1] http://www.kaltenbrunner.cc/blog/index.php?/archives/21-8.3-vs.-8.2-a-simple-benchmark.html [2] http://www.kaltenbrunner.cc/blog/uploads/83b4shm.gif [3] http://people.openwide.fr/~gsmet/postgresql/tps_shared_buffers.png (X=shared_buffers in MB/Y=results with pgbench) -- Guillaume ---------------------------(end of broadcast)--------------------------- TIP 6: explain analyze is your friend
-- Cédric Villemain Administrateur de Base de Données Cel: +33 (0)6 74 15 56 53 http://dalibo.com - http://dalibo.org
begin:vcard fn;quoted-printable:C=C3=A9dric Villemain n;quoted-printable:Villemain;C=C3=A9dric org:Dalibo email;internet:cedric.villemain@xxxxxxxxxx title:Consultant PostgreSQL tel;cell:+33 (0)6 74 15 56 53 x-mozilla-html:FALSE url:dalibo.com version:2.1 end:vcard
---------------------------(end of broadcast)--------------------------- TIP 2: Don't 'kill -9' the postmaster
