The materialized view is already optimal and cannot be tuned any further I have tried DBMS_ADVISOR.TUNE_MVIEW to verify some materialized views created locally. One of the result returns an error:

Error report:
ORA-13600: error encountered in Advisor
QSM-03116: The materialized view is already optimal and cannot be tuned any further
ORA-06512: at "SYS.DBMS_SYS_ERROR", line 86
ORA-06512: at "SYS.PRVT_ACCESS_ADVISOR", line 205
ORA-06512: at "SYS.PRVT_TUNE_MVIEW", line 951
ORA-06512: at "SYS.DBMS_ADVISOR", line 739
ORA-06512: at line 4


Does this mean the materialized view script is in the best shape, or DBMS_ADVISOR.TUNE_MVIEW is not capable to find a better solution?
If a materialized view is already fast refreshable, the DBMS_ADVISOR.TUNE_MVIEW procedure will return a message saying "the materialized view is already optimal and cannot be further tuned"

So there is nothing to do.