DBA_OUTSTANDING_ALERT records alerts

If a threshold is exceeded  or an event has occurred, MMON puts an “alert” (i.e.
message) on a predefined queue.  (This queuing mechanism uses Oracle’s
Advanced Queuing feature. )  The 10g data dictionary has been updated for alerts:
    DBA_OUTSTANDING_ALERTS describes the outstanding alerts in the
database.
    DBA_ALERT_HISTORY lists a history of alerts that have been cleared.
    V$ALERT_TYPES provides information such as group and type for each alert
We can then build notification mechanisms.  Using Oracle Enterprise Manager it’s
easy to email administrator’s if an alert occurs.
For more information on Server-Generated Alerts see Chapter 4 of the Oracle10g
Database Administrator’s Guide (“Monitoring the Operation of Your Database”).