PLPERL Function very Slow

Hi,
i am having a problem with a plperl function i am trying to write.
(using 8.1.4)

the function does a select (ca 30,000 rows) using

   spi_query($query); while (my $row = spi_fetchrow($handle))

and within the while loop inserts the record into a table using
spi_exec_query($query);

The initial select is pretty fast and first inserts very fast, but after
a few thousand inserts the inserts start to slow down until it crawls.
Writing the same in a normal perl script takes less than 90 seconds
while the function is taking 10 minutes.

My guess is that it is all memory related and was wondering if there is
a memory leak (as I read in some mails) or if there is a better way to
do what I want.

Also is there a way to commit transactions within a stored procedure /
function? I noticed that if I do a delete and insert within the same
function that the deletes are not committed until the function returns.

Thanks for any advice.

Alex