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Re: PostgreSQL performance on various distribution stock kernels

From: Greg Smith <gsmith(at)gregsmith(dot)com>
To: Damon Hart <dhcom(at)sundial(dot)com>
Cc: pgsql-performance(at)postgresql(dot)org
Subject: Re: PostgreSQL performance on various distribution stock kernels
Date: 2007-11-27 00:57:20
Message-ID: Pine.GSO.4.64.0711261937190.20455@westnet.com (view raw or flat)
Thread:
Lists: pgsql-performance
On Mon, 26 Nov 2007, Damon Hart wrote:

> Fedora 8:
> Linux 2.6.23.1-49.fc8 #1 SMP Thu Nov 8 21:41:26 EST 2007 i686 i686 i386
> GNU/Linux
>
> OpenVZ:
> Linux 2.6.18-8.1.15.el5.028stab049.1 #1 SMP Thu Nov 8 16:23:12 MSK 2007
> i686 i686 i386 GNU/Linux

2.6.23 introduced a whole new scheduler: 
http://www.linux-watch.com/news/NS2939816251.html
so it's rather different from earlier 2.6 releases, and so new that there 
could easily be performance bugs.

> Does your 10K RPM drive 166 TPS ceiling apply in this arrangement with 
> multiple disks

Number of disks has nothing to do with it; it depends only on the rate the 
disk with the WAL volume is spinning at.  But that's for a single client.

> pgbench
> scale: 50
> clients: 50
> transactions per client: 100

With this many clients, you can get far more transactions per second 
committed than the max for a single client (166(at)10K rpm).  What you're 
seeing, somewhere around 500 per second, is reasonable.

Note that you're doing two things that make pgbench less useful than it 
can be:

1) The number of transactions you're committing is trivial, which is one 
reason why your test runs have such a huge variation.  Try 10000 
transactions/client if you want something that doesn't vary quite so much. 
If it doesn't run for a couple of minutes, you're not going to get good 
repeatability.

2) The way pgbench works, it takes a considerable amount of resources to 
simulate this many clients.  You might get higher (and more realistic) 
numbers if you run the pgbench client on another system than the server.

--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD

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