Re: slow plan for min/max

On Mon, 8 Sep 2003, Neil Conway wrote:

> On Mon, 2003-09-08 at 11:56, scott.marlowe wrote:
> > 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.
>
> As was pointed out in a thread a couple days ago, MIN/MAX() optimization
> has absolutely nothing to do with MVCC. It does, however, make
> optimizing COUNT() more difficult.

Not exactly. While max(id) is easily optimized by query replacement,
more complex aggregates will still have perfomance issues that would not
be present in a row locking database. i.e. max((field1/field2)*field3) is
still going to cost more to process, isn't it?