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Fake Indexes in Oracle RDBMS (Doc ID 329457.1)

Last updated on NOVEMBER 08, 2019

Applies to:

Oracle Database - Enterprise Edition - Version to [Release 8.1.7 to 10.1]
Oracle Database Cloud Schema Service - Version N/A and later
Oracle Database Exadata Express Cloud Service - Version N/A and later
Oracle Database Exadata Cloud Machine - Version N/A and later
Oracle Cloud Infrastructure - Database Service - Version N/A and later
Information in this document applies to any platform.
Oracle RDBMS 8i, 9i and 10g.


This Note explains the concept of Fake Indexes and the causes of error ORA-8114.  These are also sometimes called Virtual Indexes.


The Oracle Enterprise Manager Tuning Wizard examines the impact on execution plans in case new indexes are created.  In order to do so, it creates a fake or virtual index on the database and checks if the new index will be used by the CBO.  Thus, it basically tricks the optimizer into believing that an index exists and generates an appropriate execution plan which enables the Enterprise Manager to analyze whether the presence of the index is going to impact the present execution plan.  Since there is no storage area associated with these indexes, they do not have any other overhead.  These fake indexes can also be used via standalone SQL*Plus.


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