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Re: Overriding the optimizer

From: "Jim C(dot) Nasby" <jnasby(at)pervasive(dot)com>
To: Mark Kirkwood <markir(at)paradise(dot)net(dot)nz>
Cc: "Craig A(dot) James" <cjames(at)modgraph-usa(dot)com>,pgsql-performance(at)postgresql(dot)org
Subject: Re: Overriding the optimizer
Date: 2005-12-16 22:45:12
Message-ID: (view raw or whole thread)
Lists: pgsql-performance
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    work: 512-231-6117
vcard:       cell: 512-569-9461

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