已經建立的index 是否有效的工作，取決于在執行SQL語句的過程，由ORACLE自己選擇是否使用index，這不由用戶決定（非強制）、但是這又是DBA想了解的。

         V$OBJECT_USAGE視圖

SQL>DESC V$OBJECT_USAGE

VIEW v$object_usage
 Name                                              Null?                     Type                       
 ----------------------------------- -------------------- ----------------------------
 INDEX_NAME                         NOT NULL        VARCHAR2(30)               
 TABLE_NAME                         NOT NULL       VARCHAR2(30)               
 MONITORING                                                    VARCHAR2(3)                
 USED                                                                  VARCHAR2(3)                
 START_MONITORING                                     VARCHAR2(19)               
 END_MONITORING                                         VARCHAR2(19)

----------------------------------------------------------------------------------------------

DBA如何監視index使用情況：

1、alter index index_name MONITORING USAGE;

2、SQL語句

3、select index_name,table_name,monitoring,used,start_monitoring,end_monoriting from v$object_usage;