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@pervasive.com
Pervasive Software      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461