||Oracle Tips by Burleson
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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