This definition appears very rarely
If yes, then AMPs retrieve the corresponding PRIMARY INDEX row_id from their subtable. Then the AMP holding the PRIMARY INDEX row_id is asked to retrieve respective records. Hence, Data Retrieval via Secondary Index is always 2 AMP or more AMP operation. For NUSI [Non Unique Secondary Index] subtable is created in the same AMP holding the PRIMARY row_id. However for USI[Unique Secondary Index], subtables hold the information about rows of different AMPs.