The dba_alert_history table has the same structure as the dba_outstanding_alerts, except for the last field. Table 4.4 describes the additional column in the dba_alert_history view.

Column	Description
RESOLUTION	Resolution -Cleared or N/A

Table 4.4 – Additional column in dba_alert_history

There are 161 metrics with definable threshold values such as physical reads per second, user commits per second, etc. For example, threshold values can be set so that an alert is sent to the DBA when the SALES tablespace exceeds 90% threshold warning level or the 96% critical level.

Alerts can also be stateless or not based on threshold levels. These stateless alerts are written directly to the history table and might include “snapshot too old” or “resumable session has been suspended.” Since OEM stores stateless alerts in its own repository, clearing the stateless alerts make sense only in OEM environment.

An alert message will be sent to the SYS owned predefined persistence queue called alert_que. Oracle Enterprise Manager (OEM) reads this queue to provide notifications about outstanding alerts, and may suggest corrective actions. The alerts are displayed on the Enterprise Manager console. OEM can be customized to send these messages to pager or email addresses. If the alert cannot be written to the queue, a message about the alert will be written to the Oracle Database alert log.