Subject: Re: enable_joinremoval
From: Simon Riggs <simon@2ndQuadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>, pgsql-hackers@postgresql.org
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Date: Mon, 29 Mar 2010 19:17:55 +0100
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On Mon, 2010-03-29 at 11:46 -0400, Tom Lane wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
> > OK, I'll write a patch for that; and a consensus emerges that we
> > should also have enable_joinremoval, then I will add that as well.  I
> > think the only argument for NOT having enable_joinremoval is that you
> > can always modify the query to say SELECT * rather than some more
> > specific SELECT list,
> 
> Uh, no, the argument for not having enable_joinremoval is that it's
> useless.
> 
> In particular, I categorically deny the argument that putting it in will
> reduce user confusion.  If anyone is confused because EXPLAIN shows that
> some table isn't getting joined to, you think that the fact that
> somewhere in the manual is a mention of enable_joinremoval will
> un-confuse them?  If they knew that switch was there or what it did,
> they wouldn't be confused to begin with.

You're not addressing the original point. I have been asked how would
users know which tables have been removed and whether there is a way of
checking that. That is not a request for a tuning feature, or something
to reduce user confusion. If you don't like "enable_joinremoval" that's
fine but it would be good to answer the original request with an
alternative proposal.

-- 
 Simon Riggs           www.2ndQuadrant.com