Fake Indexes in Oracle RDBMS
(Doc ID 329457.1)
Last updated on AUGUST 04, 2018
Applies to:Oracle Database - Enterprise Edition - Version 188.8.131.52 to 10.1.0.2 [Release 8.1.7 to 10.1]
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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