Snippet Name: INDEXES: Alter Index Deallocate Unused
Description: Use the deallocate_unused_clause to explicitly deallocate unused space at the end of the index and make the freed space available for other segments in the tablespace. If index is range-partitioned or hash-partitioned, then Oracle Database deallocates unused space from each index partition. If index is a local index on a composite-partitioned table, Oracle Database deallocates unused space from each index subpartition.
Deallocation of space is subject to the following restrictions:
- You cannot specify this clause for an index on a temporary table.
- You cannot specify this clause and also specify the rebuild_clause.
The KEEP clause lets you specify the number of bytes above the high water mark that the index will have after deallocation. If the number of remaining extents is less than MINEXTENTS, then MINEXTENTS is set to the current number of extents. If the initial extent becomes smaller than INITIAL, then INITIAL is set to the value of the current initial extent. If you omit KEEP, all unused space is freed.
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