How to optimize Postgres Database

Hi All,
I am running an application, which connects to the postgres
database at initialization time and perform the database operations like
Select/Update.
Database queries are very simple.
On analyzing my application through Quantifier( Performance analyzing
tool), I found the most of the time my application is waiting on recv,
waiting for Database response.
When i run Vacuum on perticular tables, i observed that performance
improoves drastically.

So please tell me how can i improve database performance through
configuration parameters. I had tried to change parameters in
postgresql.conf file but of no avail.
Now i am trying to Auto Vacuum, but don't know how to run Auto Vacuum.

Please help me to solve these problems.

Thanks in advance.
Hemant

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