Message-ID: <48BD42C1.6010201@enterprisedb.com>
Date: Tue, 02 Sep 2008 16:42:25 +0300
Organization: EnterpriseDB
User-Agent: Mozilla-Thunderbird 2.0.0.14 (X11/20080509)
MIME-Version: 1.0
To: Gregory Stark <stark@enterprisedb.com>
CC: Simon Riggs <simon@2ndQuadrant.com>,
	List pgsql-patches <pgsql-patches@postgresql.org>
Subject: Re: WIP Join Removal
References: <1220176372.4371.118.camel@ebony.2ndQuadrant>
	<48BC4127.30706@enterprisedb.com>
	<1220348487.4371.307.camel@ebony.2ndQuadrant>
	<48BD1374.4030504@enterprisedb.com>
	<1220352112.4371.349.camel@ebony.2ndQuadrant>
	<48BD1852.1070904@enterprisedb.com>
	<1220352898.4371.355.camel@ebony.2ndQuadrant>
	<87od36u7st.fsf@oxford.xeocode.com>
In-Reply-To: <87od36u7st.fsf@oxford.xeocode.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
From: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>

Gregory Stark wrote:
> I wonder if it would be more worthwhile to remove them and have a subsequent
> phase where we look for possible joins to *add*. So even if the user writes
> "select * from invoices where customer_id=?" the planner might be able to
> discover that it can find those records quicker by scanning customer, finding
> the matching <company_id,customer_id> and then using an index to look them up
> in invoices.

Yeah, that would be cool. The question is whether it's worth the 
additional overhead in planner, compared to the gain in the rare case 
that it's applicable. That's always the thing with planner tricks like 
this. I think we'll eventually need some sort of tuning knob to control 
how hard the planner tries to apply different optimizations like that.

-- 
   Heikki Linnakangas
   EnterpriseDB   http://www.enterprisedb.com