virtual indexes

Thought this would be  handy in testing the performance. By creating virtual indexes in a session you can check whether the performance of the bad sql can be improved or not before we implement it permanently.
this is feature is available from 11g.

ALTER SESSION SET "_use_nosegment_indexes" = TRUE;

create index vir_idx1 on Table_1 (col_1,col_2,col_3) nosegment;

once the Virtual Index is created run the bad sql and check the plan for the performance boost. if this work then create an index permanently.

Hope this helps.....