Re: Very slow joins

MS wrote:
> Btw. It looks like this issue:
> http://archives.postgresql.org/pgsql-performance/2007-09/msg00374.php
>
> In my case the CPU usage is low too (3%) but IO wait is high (95%).
>
> I'm using Postgresql 8.3.
>
>

for more info on disk iowaits, use `iostat -x 5` (5 means sample every
5 seconds), and ignore the first sample as its the average system system
boot. this will give you drive by drive and flie system by file system
details of disk IO. The exact details shown vary by operating system.

note, on many linux distributions, iostat is part of the sysstat
package, which often isn't installed by default especailly on a
'minimum' install... on RH/Fedora/Centos type systems, try `yum install
sysstat` to install it.

I never cease to be amazed at how many times people have these monster
CPUs, like dual quad core 3Ghz processors, with 16GB or whatever of ram,
and then try and run a database off a single 7200 rpm desktop SATA
drive. at work our production databases often run on dozens of 10000
or 15000 rpm drives, organized as raid1+0's.