Unable to get acceptable performance from EXCEPT

=# select count(*) from ref_old;
count
-------
10595
(1 row)

=# select count(*) from ref_new;
count
-------
22997
(1 row)

=# select ref_id from ref_old except select ref_id from ref_new;

Takes over 10 minutes, probably closer to half an hour.

I've also tried using 'NOT IN ( select ref_id from ref_new )'

ref_id is an int4, this is on Postgresql 7.0.

This confuses me because the way I'd plan to execute this query would
be something like this: (pseudo code)

result retval;
sort(ref_old);
sort(ref_new);
i = k = 0;
while (i < count(ref_old)) {
while(ref_old[i] > ref_new[k])
k++;
while(ref_old[i] == ref_new[k])
i++;
while(ref_old[i] < ref_new[k])
store(&retval, ref_old[i++]);
}
return (retval);

I can't imagine this algorithm would take over 10 minutes on my
hardware. Can anyone shed some light on what's going on here?

Is there a way to formulate my SQL to get Postgresql to follow
this algorithm?

thanks,
--
-Alfred Perlstein - [bright(at)wintelcom(dot)net|alfred(at)freebsd(dot)org]
"I have the heart of a child; I keep it in a jar on my desk."