Real-Time ADDM Connection Modes
Depending on the status of the database, ADDM uses two different connection modes in the Enterprise Manager. The normal JDBC connection is used to carry out extensive performance analyses. If the database is down and normal login is not possible, the diagnostic login mode is carried out with a latchless connection. In this mode, extreme hang situations are analyzed without exclusive access to protected resources and structures when JDBC login is no longer possible. Before 12c, the database or computer had to be restarted. Now ADDM suggests solutions without restarting the database and supports root cause analysis. The analysis information comes in real time from the SGA and includes blocking sessions, deadlocks, hangs, shared pool connections, object locks, top activities and other exceptional situations.
As of Oracle 12c, the real-time ADDM proactively detects performance problems. The Manageability Monitor (MMON) automatically collects performance statistics without locks and latches from the SGA every 3 seconds and uses the in-memory data. A diagnosis is made via performance peaks in the albania telegram screening database. The MMON slave process creates the ADDM report and saves it in the AWR repository. The report metadata is in the DBA_HIST_REPORT and ADDM views. The MMON process checks the statistics and "triggers" a real-time ADDM analysis when the incidents or problems shown in Fig. 3 occur.
Real-Time ADDM trigger control
To ensure that the automatic trigger does not use too many system resources, the real-time ADDM checks the time delta between 2 real-time ADDM reports. If the interval is less than 5 minutes, a new report is prevented from being generated. In a RAC environment, Oracle RAC takes control by running the real-time ADDM report on only one instance.