RE: ORDER BY increases consistent gets?

From: DENNIS WILLIAMS <DWILLIAMS_at_LIFETOUCH.COM>
Date: Sat, 3 Apr 2004 16:20:56 -0600
Message-ID: <0186754BC82DD511B5C600B0D0AAC4D607B0035C@EXCHMN3>

Thomas - Usually ORDER BY causes a sort to occur. A simple check would be to run EXPLAIN PLAN on both versions of the query.

Dennis Williams
DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com

-----Original Message-----

From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Thomas A. La Porte Sent: Saturday, April 03, 2004 12:25 PM
To: oracle-l_at_freelists.org
Subject: ORDER BY increases consistent gets?

Env: Oracle 8.1.7.4 on RedHat AS2.1 (2.4.9-e.35 kernel)

A developer brought me a query yesterday in which the introduction of an ORDER BY clause alters the performance substantially.

The query is as follows:

SELECT reserve_host, usage,

to_char(request_time, 'MM/DD/YYYY HH24:MI:SS') FROM licadmin.licmgr_requests

   WHERE request_time > to_date('3/14/2004', 'MM/DD/YYYY')
     AND release_time < to_date('1970', 'YYYY')
ORDER BY request_time

Without the ORDER BY clause, the query requires about 100 consistent gets, while with the ORDER BY clause it takes over 50000 consistent gets. According to autotrace and tkprof the execution plans are the same [see below].

--

Thomas A. La Porte
<mailto:tlaporte_at_yahoo.com>

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Received on Sat Apr 03 2004 - 16:21:10 CST