While observing the index statistics, you find that an index is highly fragmented, thereby resulting in poor database performance. Which option would you use to reduce fragmentation without…

ANALYZE INDEX ... VALIDATE STRUCTURE inspects the index for corruption and gathers statistics but does not reorganize or compact the index blocks to reduce fragmentation.

The ONLINE clause of ALTER INDEX ... REBUILD causes Oracle to maintain a journal of DML changes occurring during the rebuild and apply them at the end, so the existing index remains accessible throughout the operation. This removes fragmentation by creating a new, compacted index segment and then atomically replacing the old one, improving performance without blocking user access.

Changing block space utilization parameters such as PCTFREE with ALTER INDEX affects future space allocation but does not rebuild existing fragmented blocks.

ALTER INDEX ... DEALLOCATE UNUSED releases space above the index high-water mark back to the tablespace but does not consolidate fragmented leaf blocks within the used portion of the index.