Re: Optimizer picks an ineffient plan

On Wed, 3 Sep 2003, Bupp Phillips wrote:

> Well, it's unfortunate that you feel that way, because SQL Server handles it
> correctly.

For some definition of correctly. If you're in a system which gets
penalized .001 seconds for each query planning that uses a multi-column
order by and you do 100 million of them that this doesn't apply to, and
one that it does which save you 30 seconds, is that correct?

> "Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote in message
> news:4375(dot)1062643465(at)sss(dot)pgh(dot)pa(dot)us(dot)(dot)(dot)
> > Greg Stark <gsstark(at)mit(dot)edu> writes:
> > > "Bupp Phillips" <hello(at)noname(dot)com> writes:
> > >> select * from customer order by customer_id, first_name;
> > >> [ where customer_id is the primary key ]
> >
> > > However you do have a point. In this case I don't think postgres even
> > > considers using the index.
> >
> > It will not, since the index does not appear to provide the correct sort
> > order.
> >
> > > However I'm not sure I see a lot of cases where this would come up.
> >
> > Yes, that's the real crux of the matter. Should the optimizer spend
> > cycles on *every* query to detect cases where the user has written
> > useless sort keys? I've got grave doubts that it's a win. ISTM such
> > an optimization penalizes the folk who write their queries well to
> > benefit those who are careless.
> >
> > regards, tom lane
> >
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> >
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