| From: | Jaime Casanova <systemguards(at)gmail(dot)com> |
|---|---|
| To: | "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com> |
| Cc: | Mark Kirkwood <markir(at)paradise(dot)net(dot)nz>, "Craig A(dot) James" <cjames(at)modgraph-usa(dot)com>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Overriding the optimizer |
| Date: | 2005-12-17 12:31:40 |
| Message-ID: | c2d9e70e0512170431m1275018cq363851364cdbb54b@mail.gmail.com |
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| Lists: | pgsql-performance |
> > 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.
Plan stability doesn't mean time response stability...
The plan that today is almost instantaneous tomorrow can take hours...
--
regards,
Jaime Casanova
(DBA: DataBase Aniquilator ;)
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