SQL> select * from v$object_usage

INDEX_NAME TABLE_NAME  MON USE START_MONITORING    END_MONITORING
---------- ----------- --- --- ------------------- --------------
IDX1       IDXTEST     YES NO  06/07/2009 19:20:58
IDX2       IDXTEST     YES NO  06/07/2009 19:21:04

SQL> alter index IDX1 rebuild;

Index altered.

SQL> alter index IDX2 rebuild online;

Index altered.

SQL> select * from v$object_usage;

INDEX_NAME  TABLE_NAME  MON USE START_MONITORING    END_MONITORING
----------- ----------- --- --- ------------------- --------------
IDX1        IDXTEST     NO  YES 06/07/2009 19:20:58
IDX2        IDXTEST     NO  NO  06/07/2009 19:21:04

So, the commands “ALTER INDEX … REBUILD” and “ALTER INDEX … REBUILD ONLINE” both set the Mon(itor) flag to NO. Moreover the “ALTER INDEX .. REBUILD” also sets the USE Flag to YES.

I have found this information in Norbert Debes book “Secrets of the Oracle Database”.

thank you for contribution. See you in Zurich.

Martin

Another case where MONITORING USAGE does a bad job is when an index is used to check a foreign key.
So, all in all, MONITORING USAGE might help but we cannot simply take the information it provides without assessing what they really mean…

Cheers,
Chris