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Re: graph representation of data structures in optimizer

From: Gregory Stark <stark(at)enterprisedb(dot)com>
To: Adriano Lange <adriano(at)c3sl(dot)ufpr(dot)br>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: graph representation of data structures in optimizer
Date: 2009-02-18 16:19:09
Message-ID: 87zlgjzpj6.fsf@oxford.xeocode.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Adriano Lange <adriano(at)c3sl(dot)ufpr(dot)br> writes:

> Hi,
>
> I'm interested in data representation and debug of optimizer routines. Thus,
> I've changed the debug functions of allpaths.c to make a graphviz-like output
> of RelOptInfo structure.
>
> Any idea about this?
> Is there some project or improvement like this?

Several people have asked about ways to see what possible plans were
considered and why the were rejected, it was one of the repeat offenders in
the recent Postgres Pet Peeves thread so this is a very interesting area to
explore.

However I have to say this graph you've generated is amazingly hard to
decipher :) It took me a while to even figure out what information it was
presenting.

Worse, it's not useful unless you add a lot more information to it such as
what relations are actually being scanned or joined at each path which is
going to make it a hell of a lot harder to read.

I'm not sure how to do any better but I would be fascinated to see any new
images you generate :)

-- 
  Gregory Stark
  EnterpriseDB          http://www.enterprisedb.com
  Ask me about EnterpriseDB's PostGIS support!

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