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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: (view raw, whole thread or download thread mbox)
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 
 PostgreSQL Training, Services and Support

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