Why different execution times for different instances for the same query?

Hi All,

I am Kishore doing freelance development of J2EE applications.

We switched to use Postgresql recently because of the advantages it has
over other commercial databases. All went well untill recently, untill we
began working on an application that needs to maintain a huge database.

I am describing the problem we are facing below. Can you please take a look
at the case, and help me in resolvign the issue.

We are executing a single query that returned very fast on the first
instance. But when I executed the same query for multiple times, it is
giving strange results. It is not coming back.
When I checked with the processes running in the system, I observed that
multiple instances of postmaster are running and all of them are consuming
very high amounts of memory. I could also observe that they are sharing the
memory in a uniform distribution across them.
Can you please let me know if you have experienced the same and how do you
resolved it?
Thank you,
Kishore.