ADDM (Automated Database Diagnostic Monitor) is available since Oracle 10g.
are useful features for performance tuning and troubleshooting.
ADDM reports the most significant performance problems between AWR snapshots.
Whether a performance problem is captured by ADDM depends then on its duration compared to the interval between AWR snapshots (default of one hour)
ADDM analyses a number of database-related problems
You can use Oracle Enterprise Manager (OEM) to view the ADDM findings.