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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: 20051216224512.GX53809@pervasive.com (view raw or flat)
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      http://pervasive.com    work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf       cell: 512-569-9461

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