HEIGHT:
This column refers to the height of the B-tree index,and it's usually at the 1,2,or 3 level.
If large inserts push the index height beyond a level of 4,it's time to rebuild,which flattens the B-tree. DEL_LF_ROWS:
This is the number of leaf nodes deleted due to the deletion of rows.
Oracle doesn't rebuild indexes automatically and,consequently,too many deleted leaf rows can lead to an unbalanced B-tree. BLK_GETS_PER_ACCESS:
You can look at the BLK_GETS_PER_ACCESS column to see how much logical I/O it takes to retrieve data from the index. If this row shows a double-digit number,you should probably start rebuilding the index.

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