What is postmaster doing?

Folks,

I am running into a problem with the postmaster: from time to time, it
runs for a long time. E.g., from top:

23425 postgres  20   0 22008  10m  10m R 99.9  0.5  21:45.87 postmaster

I'd like to figure out what it is doing. How can I figure out what
statement causes the problem?

is there a way I can log all SQL statements to a file, together with the
time it took to execute them?

--
Dimi Paun <dimi@lattica.com>
Lattica, Inc.