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Alteration of Indexes

If the DBA suspects that an index’s storage clause is improper, he or she can run the script in Source 6.4 to show the space used for the average entry in the index. This data can then be input to the space calculation formula to get a more accurate sizing estimate. The DBA can then use the ALTER INDEX command to alter the index’s storage clause for future extents, or drop and re-create the index with better parameters.     

Indexes can be altered to change their storage clauses, and in version 7.3.4 and all 8 versions, they can be rebuilt on the fly. Oracle8i and Oracle also allow either online (where table access is permitted) or offline (where table access is restricted). The alteration will affect only the storage allocations of future extents. To alter rows used in the index, unique versus nonunique, or all of the storage extents for an existing index, it must be dropped and re-created. To alter the storage within an existing index, use the ALTER INDEX command.

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