052-3

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 affecting the users who are currently using the index?
A.Validate the index structure using the ANALYZE...INDEX command.
B.Rebuild the index using the ALTER INDEX..REBUILD ONLINE command.
C.Change the block space utilization parameters using the ALTER INDEX command.
D.Deallocate the unused space in the index using the ALTER INDEX..DEALLOCATE UNUSED command.

由于频繁的 dml，索引就会产生碎片，它的效率会越来越慢，因此就需要重建，可以使用 online 关键字在线重建索引，因为重建索引的时候会加锁，假如该关键字后，可以使加锁时间变的很短，从而减少对使用索引用户的影响