One feature I would really like to see PG use from Oracle is Index Only Tables. They tend to speed up searches on existance for certain keys by a large factor. In the current PG structure an index node may not be valid and you must check the corresponding table to see if an index node does exist. In a heavily volatile system many index may indeed be no longer valid. Remember that vacuum does not shrink indexes either.
There was a patch that kinda started adding it but it doesnt seem to have been picked up and developed more. For more info check out
pgsql is 75 times faster with my new index scan thread on hackers list.
