Using PL/SQL Packages for Server Generated Alerts

The threshold settings can be changed as needed using the above referenced PL/SQL procedures or OEM. OEM functionalities can also be used to set up notification rules. OEM will display the alert in its console and will notify the administrators registered to receive alerts.  There is no PL/SQL procedure provided to set thresholds based on baselines.  DB Control has a screen that shows the metric values based on baselines. 

The amount that thresholds are to be higher or lower than the baseline values can be specified by percentage.  DB Control then sets the thresholds using the derived values for each metric using the DBMS_SERVER_ALERT.SET_THRESHOLD procedure. All thresholds except for space related alerts should be explicitly defined. Set the statistical_level initialization parameter to TYPICAL or ALL.

The metric values are regularly calculated by MMON and kept in memory for an hour. These in-memory values can be queried from the v$sysmetric and v$sysmetric_history views. By enabling the automatic snapshot mechanism of AWR, these metrics can be collected on disk. The on-disk values can be viewed from dba_hist_* views. Remember that the metric history is purged periodically like other snapshots.

v$alert_types, dba_outstanding_alerts, dba_alert_history, and dba_thresholds are some of the dictionary views used to view alert information.  Note the following: