Cannot Achieve Performance

Dear all,

Performance tuning is what, which all i sured to achieve in pgsql. I am
currently testing on 5 GB table with select operation that takes about
229477 ms ( 3.82 minutes  ) with simple configuration.

I have 4 GB RAM. So I change some parameters such as  shared_buffers to
512 MB , effective cache  size to 1024 MB and my separate log directory.

Would this is sufficient or I need something else to be changed.

But my output after changing these parameters is not what I am expecting
of , it is 229971 ms ( 3.81 minutes ). Please help.

Waiting for some pointers until I am googling.

Thanks & Regards

Adarsh Sharma