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Added column to existing index vs creating new index

edited Apr 17, 2018 1:32PM in Database Tuning (MOSC) 9 commentsAnswered ✓

Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production    

TNS for Linux: Version 12.2.0.1.0 - Production  

We are running an OLTP system, which is tuned for high inserts/updates.  Performance for inserts/updates remains the priority.  However, we have some queries that must be run, that are performance hogs.  Index changes are in order to support the query.  Is there less maintenance overhead to add a 3rd column to an existing composite index?  Or add a new, single-column index.  The query benefits from either option are roughly equal.  The argument that tips the balance is cost of index maintenance.

Existing composite index is (varchar2(1), number(19).  Looking to change it to (varchar2(1), number(19), varchar2(40), or just creating a new (varchar2(40) index.

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