On Sun, 7 Sep 2003, Pailloncy Jean-Gérard wrote:
Asking a question about why max(id) is so much slower than select id order
by id desc limit 1, Pailloncy said:
> I ask for the same thing.
> That's better !
This is a Frequently asked question about something that isn't likely to
change any time soon.
Basically, Postgresql uses an MVCC locking system that makes massively
parallel operation possible, but costs in certain areas, and one of those
areas is aggregate performance over large sets. MVCC makes it very hard
to optimize all but the simplest of aggregates, and even those
optimzations which are possible would wind up being quite ugly at the
parser level.
You might want to search the archives in the last couple years for this
subject, as it's come up quite often.