Memory not released immediately with named cursors

I changed the test_fetch() function to release the memory.
For some reason, "del big_var" is not enough. A "gc.collect()" call is required.

def test_fetch(cursor):
    big_var = range(1 << 23)
    del big_var
    gc.collect()
    cursor.fetchone()

$ python --version Python 2.6.6
$ python testmem.py psycopg2 version 2.4.5 (dt dec pq3 ext)
Record size: 1024 B; Memory used: 8.8 MB
Record size: 16339 B; Memory used: 8.8 MB
Record size: 16340 B; Memory used: 8.8 MB
$

So it's no link in psycopg, just the way the python gc works, right?

I am running this on Debian Squeeze.
It's possibly related to the way the memory is allocated then released.

I don't have other test case than the "testmem.py" above.
Could be closed, since I managed to deal with named cursors without any other memory issue.