Oracle-L: RE: Index & Constraint

From: <Rajesh.Rao_at_jpmchase.com>
Date: Fri, 07 Jun 2002 13:43:50 -0800
Message-ID: <F001.00477F65.20020607134350@fatcity.com>

An example on my understanding of Reverse Key Indices:

Say you have a table EMP with a column EMPNO, and an index on this field.This number is incremented sequentially for every new employee that joins in. And as employees retire, say, the records are deleted. This would generally mean deletion of records, with lower employee numbers. And subsequent deletion of indices. As such, deletions from the index are likely to be concentrated on a small set of leaf blocks towards the beginning of the index. A reverse key index, which reverses the bytes for the column value, could help in uniformly dividing the deletions across various branches of the index, and avoid a skewed index.

Raj

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                    "Jamadagni,                                                                                           
                    Rajendra"                  To:     Multiple recipients of list ORACLE-L <ORACLE-L_at_fatcity.com>        
                    <Rajendra.Jamadagni        cc:                                                                        
                    @espn.com>                 Subject:     RE: Index & Constraint                                        
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                    June 07, 2002 04:33                                                                                   
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No, don't use reverse index for FKs, on certain versions they caused havoc by allowing parent key to be deleted (Metastink has an alert on this one). Reverse indexes are preferred in OPS environment AFAIK.

Raj

Rajendra Jamadagni                  MIS, ESPN Inc.

Rajendra dot Jamadagni at ESPN dot com
Any opinion expressed here is personal and doesn't reflect that of ESPN Inc.

QOTD: Any clod can have facts, but having an opinion is an art!
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Received on Fri Jun 07 2002 - 16:43:50 CDT