RMAN works best with RBO

Eventhough Oracle forced everyone to move to Cost Based Optimizer (CBO), their own tools continue to use RBO. RMAN is a classic example. Refer to Metalink Note 375386.1 which describes performance problems selecting from V$RMAN_STATUS. The cause is given as bug 5247609 and workaround provided is:

Add the following to your rman script:

sql "alter session set optimizer_mode=RULE";

A few customers have found that using RULE does not workaround this but gathering fixed statistics does:

SQL> exec dbms_stats.gather_fixed_objects_stats()