Same SQL statement, Same Oracle, Different OS ==> Different Expla

From: Sam Bootsma <SamB_at_cpas.com>
Date: Fri, 06 Sep 2002 10:36:56 -0800
Message-ID: <F001.004CA1E9.20020906103656@fatcity.com>

Hello everybody,

One of our developers is encountering a situation where Oracle 9.0.x explain plan chooses one index when on UNIX, and chooses a different index when running on Windows NT. I'd appreciate any insights or similar experiences.

The following are the facts:
1. The explain plan is run against the same SELECT statement on both platforms
2. It has been confirmed that there are no statistics on either of the databases
3. Both databases are using RBO (not CBO) 4. The UNIX database has about 100 times as many rows (in this table) as the NT database
5. The SELECT statement that gives different explain plans on different platforms is:

SELECT FN.*, FN.ROWID
FROM UNITFUND FN
WHERE FN.FU_CODE = :cFuCode AND

FN.MKEY = :cMkey AND
FN.CLNT = :sKey AND
FN.PLANNO = :sKey AND
FN.DATE_FROM <= :dDate AND
FN.SOURCE = :cSource AND
FN.TSTATUS  =  'O'

ORDER BY FN.DATE_FROM, FN.TSECOND; 6. Between the following 2 indexes, Oracle 9.0x chooses (2) on Unix and (1) on Windows NT.

clnt, mkey, planno, fu_code, date_from, source, tracode, tsecond...
date_from, clnt, planno, mkey, fu_code

Any insights from anybody out there? Thanks.

Sam Bootsma, OCP
Technical Support Analyst

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Author: Sam Bootsma
INET: SamB_at_cpas.com

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