When to rebuild an index

• The existing index needs to be moved to a different tablespace. This may be necessary if the index is in the same tablespace as the table or if objects need to be redistributed across disks
• An index contains many deleted entries
• An existing normal index needs to be converted into a reverse key index. This may be the case when migrating applications from an earlier release of the Oracle server
• The table of the index has been moved to another tablespace using the ALTER TABLE ... MOVE TABLESPACE command