Tuning configuration

Hello,

I have a hopefully simple question. I've found documentation about
the meanings of the various variables in postgres.conf -- if it comes
to memory consumption and buffer size. I've also found hints as to
making them too large decreases performance. But -- how can I measure
how well the current settings fit? Are there tables to watch on how
quickly things like temp tables get written out to disk vs. being held
in memory? We'd like to find an appropriate size for our database,
but can't even yet say if we're in the right ballpark on a machine
that has RAM to spare still.

What can I look into?

Thank you,
Konrad Neuwirth