Column USERNAME and SESSION_INFO are UNKNOWN or NULL in V$LOGMNR_CONTENTS [ID 110301.1]
You have just built the LogMiner dictionary and started LogMiner.  You query V$LOGMNR_CONTENTS expecting to see the USERNAME and SESSION_INFO for some particular redo or undo operation. However, the USERNAME field is NULL.  This is NOT a recursive operation, and the USERNAME column is expected to contain a non-null value.
Solution:=========This can result from your database parameter settings and also from the methodyou are using to mine redo logs using LogMiner.
1. Ensure that database was in minimum supplemental logging at the time that   the redo information was created.  
2. Ensure that all archive redo logs containing the necessary redo   information have been added to the LogMiner session.
1.也就是需要添加supplemental log;
sql>ALTER DATABASE ADD SUPPLEMENTAL LOG DATA; #11g建议是alter database add supplemental log data (primary key,unique index) columns;
10.2.0.1有可以ALTER DATABASE ADD SUPPLEMENTAL LOG DATA; 时可能会报ora-600或hang住,一般启动到mount下就可解决.
STARTUP MOUNT
ALTER DATABASE ADD SUPPLEMENTAL LOG DATA;
ALTER DATABASE OPEN;