Slow rman Backups? Check This Out

If you have found rman backups slow in Oracle 10.2.0.2, you should check out note 375386.1 on metalink. It seems the CBO isn’t all its made out to be, and you have to force rman to use the RULE hint instead to make your rman backup run faster. (And you thought RULE was deprecated, didn’t you!)

A few interesting things come out of that Oracle note.

1. Tracing an rman session: connect to rman and set a 10046 event:

   rman target / log rman.log trace rman.trc debug
   RMAN> sql "alter session set events ' '10046 trace name context forever, level
   12' '"

   Note the two single quotes before 10046 and two single quotes and a double quote after level 12

2. Setting rman to use the RULE hint instead of CBO: add the following to your rman script:

   sql "alter session set optimizer_mode=RULE";

3. In spite of what Oracle says, there really is no end of the road for the RULE hint just yet.

The underlying bug# is 5247609 if you’re interested.