OCP 1Z0 052 V9.02 72

72.Examine the following output:  
SQL> SELECT index_name,status  
FROM dba_indexes  
WHERE status='UNUSABLE';  
INDEX_NAME STATUS  
EIND UNUSABLE  
Which two statements about the above index are true? (Choose two.)  
A. It is ignored by the query optimizer.  
B. It is not used while the index is being rebuilt.  
C. The index cannot be rebuilt, and has to be re-created.  
D. The index is automatically rebuilt when used the next time.  
Answer: AB  

dml不维护不可用索引，在进行大量dml操作前可以把索引设为不可用，以增加dml速度，待操作完成再对索引rebult

unusable index

An index that is not maintained by DML operations and is ignored by the optimizer. All indexes are usable (default) or unusable.