8.4/9.0 simple query performance regression

All,

Just got this simple case off IRC today:

8.4.4
This plan completes in 100ms:

old_prod=# explain analyze select email from u_contact where id not in
(select contact_id from u_user);
QUERY PLAN

--------------------------------------------------------------------------------------------------------------------
Seq Scan on u_contact (cost=2217.72..4759.74 rows=35560 width=22)
(actual time=61.283..107.169 rows=4521 loops=1)
Filter: (NOT (hashed SubPlan 1))
SubPlan 1
-> Seq Scan on u_user (cost=0.00..2051.38 rows=66538 width=8)
(actual time=0.034..33.303 rows=66978 loops=1)
Total runtime: 108.001 ms

9.0.2
This plan does not complete in 15 minutes or more:

new_prod=# explain select email from u_contact where id not in (select
contact_id from u_user);
QUERY PLAN
---------------------------------------------------------------------------
Seq Scan on u_contact (cost=0.00..100542356.74 rows=36878 width=22)
Filter: (NOT (SubPlan 1))
SubPlan 1
-> Materialize (cost=0.00..2552.56 rows=69504 width=8)
-> Seq Scan on u_user (cost=0.00..1933.04 rows=69504 width=8)
(5 rows)

I'm at a bit of a loss as to what's happening here. I'd guess another
failure of a bail-out-early plan, but I can't see how that would work
with this query.

--
Josh Berkus
PostgreSQL Experts Inc.
http://pgexperts.com