how to determine an index need to be rebuild

Is an index required to be rebuilt? We can check a post regarding this:

Richard Foote's Oracle Blog

Indexes will occupy a lot of space, so you can check whether it was being used. For this you can check out for v$object_usage. If needed you can also enable Monitoring usage of indexes by using 

Alter index enable Monitoring Usage ; 

If there is Fragmentation of Index then it needs to be rebuilt. Refer the above link mentioned in this discussion which is a very useful one.

We can check if an index needs to be rebuilt by executing the following statements:


ANALYZE INDEX index_name VALIDATE STRUCTURE;

SELECT HEIGHT, DEL_LF_ROWS, LF_ROWS, LF_BLKS FROM INDEX_STATS;
If the value for DEL_LF_ROWS/LF_ROWS is greater than 2, or LF_ROWS is lower than LF_BLKS, or HEIGHT is 4 then the index should be rebuilt.