From: Jim C. Nasby <jnasby@pervasive.com>
To: Jaime Casanova <systemguards@gmail.com>
Cc: Mark Kirkwood <markir@paradise.net.nz>
Cc: Craig A. James <cjames@modgraph-usa.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: Overriding the optimizer
Date: Tue, 20 Dec 2005 12:56:18 -0600
Message-ID: <20051220185618.GE28771@pervasive.com> (raw)
In-Reply-To: <c2d9e70e0512170431m1275018cq363851364cdbb54b@mail.gmail.com>
References: <1134629567.14248.27.camel@firebolt>
<200512150148.16125.blargity@gmail.com>
<1134644526.14248.60.camel@firebolt>
<43A1C40D.8040006@paradise.net.nz>
<43A1F6DB.3080805@modgraph-usa.com>
<43A226E7.7040508@paradise.net.nz>
<43A22BE3.6020103@modgraph-usa.com>
<43A231AA.9070708@paradise.net.nz>
<20051216224512.GX53809@pervasive.com>
<c2d9e70e0512170431m1275018cq363851364cdbb54b@mail.gmail.com>
On Sat, Dec 17, 2005 at 07:31:40AM -0500, Jaime Casanova wrote:
> > > 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...
Sure, if your underlying data changes that much, but that's often not
going to happen in production systems (especially OLTP where this is
most important).
Of course if you have a proposal for ensuring that a query always
finishes in X amount of time, rather than always using the same plan,
I'd love to hear it. ;)
--
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: jnasby@pervasive.com, systemguards@gmail.com, markir@paradise.net.nz, cjames@modgraph-usa.com
Subject: Re: Overriding the optimizer
In-Reply-To: <20051220185618.GE28771@pervasive.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox