Exadata Storage Index and Smart scan goes hand in hand :

In my earlier Post we saw that we cannot use storage Indexes if our smart scan doesn't happen:

A little explanation:
If optimizer have decided not to do direct path read then storage index cannot be used as you know direct path read of mandatory required for Smart Scan, Also there can be other reasons when Smart Scan cannot be used. Reason for this is Smart Scan send the iDB message to Storage server and cellsrv process detects the additional information to process its data and so cellserver can effectively detect which part of storage to access more precisely which rows to be accessed from particular storage region . So if smart scan dosn't happen which also means no additional information inform of iDB message then cellserver cann't filter out the data. So please make a note of it. Also my following example shows this behavior.

To disable Storage index usage we can use following parameter a session level:
SQL>alter session set "_kcfis_storageidx_disabled"=TRUE;


This parameter actually doesn't drop the Storage index but however hided from been used by smart scan.