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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>