Measurement tool for POSTGRES

Hi everyone,

This is my first post to the list so excuse me if the question is not appropriate
for this list.
I am connecting to the postgres database trough JDBC from servlets. Everything is
working OK but sometimes the system crashes due to heavy load. Our server is hosting a
lot of websites and some of them are doing extensive database querying.
I am looking for a tool that shows how many open connections are in postgres. Also is it possible
to set how many open connection can be ? In a few servlets we are not closing the connection
for a very long time to have faster database access.

Any help is appreciated.

Thank You,

Andras.