From: worky.workerson@gmail.com
To: pgsql-performance@postgresql.org
Subject: Self-join query and index usage
Date: 14 Jul 2006 11:56:53 -0700
Message-ID: <1152903413.210226.284600@75g2000cwc.googlegroups.com> (raw)
I'm doing a self join of some shipping data and wanted to get the best
query possible. The interesting table is the event table, and it has
the following structure:
startnode int,
endnode int,
weight int,
starttime timestamp,
endtime timestamp
and the query that I would like to run is:
SELECT e1.endnode, count(*), sum(e1.weight) AS weight1, sum(e2.weight)
AS weight2
FROM event e1, event e2
WHERE e1.endnode = e2.startnode AND e1.starttime < e2.starttime AND
e2.starttime < e1.endtime
GROUP BY e1.endnode
Assuming that I have indexes on all the columns, should this query be
able to make use of the indexes on starttime and endtime?
The "best" plan that I could see is a merge join between a sorted
sequential scan on e2.startnode and an index scan on e1.endnode, which
I figure takes care of the "e1.endnode = e2.startnode". The join
filter is then "e1.starttime < e2.starttime AND e2.starttime <
e1.endtime" ... does this use an index? Can the planner to use a
bitmap index scan to use the indexes on the start/endtimes in the join?
Table is about 3GB.
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To: pgsql-performance@postgresql.org
Cc: worky.workerson@gmail.com
Subject: Re: Self-join query and index usage
In-Reply-To: <1152903413.210226.284600@75g2000cwc.googlegroups.com>
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