stored procedure code

Hi=2C I would like to learn about how stored procedures are handled in post=
gres. In particular=2C I'd like to learn how plpgsql procedures are compile=
d and stored=2C and how they (both plpgsql and C procedures) interact with =
the optimizer during planning. Would appreciate if someone can point out so=
me links to the source code for me to check out.
Thanks!Derek                           =