transaction control in pl/pgsql

Dear list,

I have some data (big size) and I've written a long function in pl/pgsql
which processes the data in several steps. At a test run my function
aborted because of memory exhaustion. My guess is, that everything what
happens during the function transaction is stored in the memory - until
it's full... So, my idea for solving that problem would be to cut the
big function into smaller functions. But, I don't want to write 30
function calls at the end - I would rather like to have one function
which is calling all these small functions, so I would only have to
write one sql-query at the end. What I fear is either, that, if this
function calls the other functions, everything is only one trancaction
again and I get memory overflow once more.

I've read the documentation regarding this on
http://www.postgresql.org/docs/8.4/interactive/plpgsql-structure.html :

"It is important not to confuse the use of BEGIN/END for grouping
statements in PL/pgSQL with the similarly-named SQL commands for
transaction control. PL/pgSQL's BEGIN/END are only for grouping; they do
not start or end a transaction. Functions and trigger procedures are
always executed within a transaction established by an outer query —
they cannot start or commit that transaction, since there would be no
context for them to execute in."

Somewhere else I've read: "PostgreSQL does not have nested transactions."

I'm still not sure if I got it right or if there are other possibilities
to solve my problem. Any suggestions would be appreciated!

Thanks and regards,

Birgit.