One of the background database processes that shouldn't occupy too much of your system is the statistics collector, which looks like this from the perspective of ps:
Postgres 32450 32445 0 13:49 ? 00:00:00 postgres: stats collector process
Under normal circumstances, the statistics collection shouldn't take more than a few percent of CPU time even under heavy activity. There are occasional versions of PostgreSQL where this is not true. For example, 8.2.0 through 8.2.3 had a serious bug where statistics wrote far too often. But even if you're running 8.2, you should never be using such an old minor release of it, anyway.
Sometimes, circumstances aren't normal enough and the statistics collector takes up ...
