postgres on apple OS X server

Hi,

I have a postgres database that is VERY slow - in one table we have 50
mil records in it.
I have tried to play with postgres.conf file and shared memory but was
not able to speed it up to something that we can work with. We have
apple RAID and I am planning to take database to the raid. I was
wondering if someone has any hints about improving the speed on postgres.

Currently we have:
shmall = 134217728
shmmax = 134217728

and in postgresql.conf I was setting up values to:
shared_buffers = 15200
sort_mem = 32168

Can someone please help me to tune up this database?

Thanks a lot for your help,

Mira

P.S. Please reply also to mkaloper(at)ucdavis(dot)edu