Re: Overriding the optimizer

On Fri, Dec 16, 2005 at 04:16:58PM +1300, Mark Kirkwood wrote:
> Craig A. James wrote:
>
> >
> >What would be cool would be some way the developer could alter the plan,
> >but they way of doing so would strongly encourage the developer to send
> >the information to this mailing list. Postgres would essentially say,
> >"Ok, you can do that, but we want to know why!"
> >
>
> Yeah it would - an implementation I have seen that I like is where the
> developer can supply the *entire* execution plan with a query. This is
> complex enough to make casual use unlikely :-), but provides the ability
> to try out other plans, and also fix that vital query that must run
> today.....

Being able to specify an exact plan would also provide for query plan
stability; something that is critically important in certain
applications. If you have to meet a specific response time requirement
for a query, you can't afford to have the optimizer suddenly decide that
some other plan might be faster when in fact it's much slower.
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461