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Re: Planner creating ineffective plans on LEFT OUTERjoins

From: Simon Riggs <simon(at)2ndquadrant(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Andres Freund <andres(at)anarazel(dot)de>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Planner creating ineffective plans on LEFT OUTERjoins
Date: 2008-06-26 08:15:13
Message-ID: 1214468113.3845.10.camel@ebony.site (view raw or flat)
Thread:
Lists: pgsql-hackers
On Wed, 2008-06-25 at 23:34 -0400, Robert Haas wrote:
> I can predict that Tom will say that the planning time it would take
> to avoid this problem isn't justified by the number of queries that it
> would improve.  

> That's possible, but it's unfortunate that there's no
> way to fiddle with the knobs and get the planner to do this kind of
> thing when you want it to.

I don't think we should invent a new parameter for each new
optimisation. We would soon get swamped.

IMHO we should have a single parameter which indicates how much planning
time we consider acceptable for this query. e.g.

 optimization_level = 2 (default), varies 1-3

Most automatic optimisation systems allow this kind of setting, whether
it be a DBMS, or compilers (e.g. gcc). 

We should agree a simple framework so that each new category of
optimization can be described as being a level X optimisation, or
discarded as being never worth the time. We do this with error messages,
so why not do this with something to control planning time?

-- 
 Simon Riggs           www.2ndQuadrant.com
 PostgreSQL Training, Services and Support


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