Re: Scaling SELECT:s with the number of disks on a stripe

On 2007-04-04, Peter Schuller <peter(dot)schuller(at)infidyne(dot)com> wrote:
>> The next question then is whether anything in your postgres configuration
>> is preventing it getting useful performance from the OS. What settings
>> have you changed in postgresql.conf?
>
> The only options not commented out are the following (it's not even
> tweaked for buffer sizes and such, since in this case I am not
> interested in things like sort performance and cache locality other
> than as an afterthought):
>
> shared_buffers = 1000

I'd always do benchmarks with a realistic value of shared_buffers (i.e.
much higher than that).

Another thought that comes to mind is that the bitmap index scan does
depend on the size of work_mem.

Try increasing your shared_buffers to a reasonable working value (say
10%-15% of RAM - I was testing on a machine with 4GB of RAM, using a
shared_buffers setting of 50000), and increase work_mem to 16364, and
see if there are any noticable changes in behaviour.

--
Andrew, Supernews
http://www.supernews.com - individual and corporate NNTP services