From: Tom Lane <tgl@sss.pgh.pa.us>
To: Simon Riggs <simon@2ndQuadrant.com>
Cc: List pgsql-patches <pgsql-patches@postgresql.org>
Subject: Re: WIP Join Removal
Date: Tue, 02 Sep 2008 12:35:21 -0400
Message-ID: <15301.1220373321@sss.pgh.pa.us> (raw)
In-Reply-To: <1220176372.4371.118.camel@ebony.2ndQuadrant>
References: <1220176372.4371.118.camel@ebony.2ndQuadrant>
Simon Riggs <simon@2ndQuadrant.com> writes:
> + if (removable &&
> + joinrel->cheapest_total_path < keeprel->cheapest_total_path)
> + {
> + elog(LOG, "join removed");
> + joinrel->pathlist = keeprel->pathlist;
> + joinrel->joininfo = keeprel->baserestrictinfo;
> + }
> + }
On third thought: if you think that the join paths could possibly win,
then the correct coding here is something like
foreach(path, keeprel->pathlist)
add_path(joinrel, ...)
The reason is that it's not an all-or-nothing choice: some of the paths
might offer cheaper startup cost, or present a useful sort order.
So just present them as available alternatives and let add_path sort it
out.
regards, tom lane
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To: pgsql-patches@postgresql.org
Cc: tgl@sss.pgh.pa.us, simon@2ndQuadrant.com
Subject: Re: WIP Join Removal
In-Reply-To: <15301.1220373321@sss.pgh.pa.us>
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