postgresql 7.4.6 slowing down

I'm using Fedora Core 2, apache 2.0 and postgresql 7.4.6.
Recently, the application is slowing down. When I check the process
using "top", sometimes postmaster process time is increasing and the
process is never end, I think this cause the application slowing down
and sometimes this process make the server slowing down and I have to
restart postmaster.
Is there somebody who experience the same problem? and what is the solution?

Thank You,

Frans