Nested Transactions in PL/pgSQL

Is it possible to nest transactions within a stored procedure? I have a
stored procedure that calls many other stored procedures and what
happens it that after a certain amount of time the server runs out of
shared memory. I know I can increase the PostgreSQL shared memory.
However, that would be a temporary fix. I know it will eventually run
out again as more data is processed. The right way to do it is to do
issue a save point or commit at various places in my long stored
procedure. I want to believe that there is a way to issue commits
within a stored procedure since PostgreSQL now supports nested
transactions.

Any help or work around would be appreciated. Thanks.

Andy Nykolyn
Northrop Grumman