IN() Optimization issue in 8.0rc5

Tom,

Hmmm ... I'm seeing an issue with IN() optimization -- or rather the lack of
it -- in 8.0rc5. It seems to me that this worked better in 7.4, although
I've not been able to load this particular database and test

dm=# explain
dm-# SELECT personid FROM mr.person_attributes_old
dm-# WHERE personid NOT IN (SELECT
personid FROM mr.person_attributes);
QUERY PLAN
-----------------------------------------------------------------------------------
Seq Scan on person_attributes_old (cost=0.00..3226144059.85 rows=235732
width=4)
Filter: (NOT (subplan))
SubPlan
-> Seq Scan on person_attributes (cost=0.00..12671.07 rows=405807
width=4)
(4 rows)

dm=# explain select pao.personid from mr.person_attributes_old pao
dm-# left outer join mr.person_attributes p on pao.personid = p.personid
dm-# where p.personid is null;
QUERY PLAN
---------------------------------------------------------------------------------------------------------------
Merge Left Join (cost=0.00..34281.83 rows=471464 width=4)
Merge Cond: ("outer".personid = "inner".personid)
Filter: ("inner".personid IS NULL)
-> Index Scan using idx_opa_person on person_attributes_old pao
(cost=0.00..13789.29 rows=471464 width=4)
-> Index Scan using idx_pa_person on person_attributes p
(cost=0.00..14968.25 rows=405807 width=4)
(5 rows)

It seems like the planner ought to recognize that the first form of the query
is optimizable into the 2nd form, and that I've seen it do so in 7.4.
However, *no* amount of manipulation of query parameters I did on the 1st
form of the query were successful in getting the planner to recognize that it
could use indexes for the IN() form of the query.

Thoughts?

--
Josh Berkus
Aglio Database Solutions
San Francisco