Emergency Monitoring feature of EM Cloud allows for DBA to connect to non-responding database by way of proprietary resources for diagnosis of problem. The EM agent connects directly to SGA, bypassing the SQL retrieval layer. The page displays ASH data and Hang Analysis table, displaying blocking sessions and allows for killing this blocks. Emergency Monitoring page is accessible from Performance Menu of EM Cloud. EM Express has no diagnostic connection.
Real-Time ADDM – introduced in EM Cloud 12c, much of functionality is available in EM Express. ADDM is to help with analysis of problem which cause unresponsive behavior without restarting DB. ADDM checks for problems based on set of predefined criteria, then suggests solutions.
Two Ways ADDM connects:
- Normal Connection – normal JDBC connection, used for extensive performance analysis.
- Diagnostic Connection – latchless connection for hung situations, where JDBC connection is not available.
Differences between REAL-Time ADDM and ADDM
- Real-Time ADDM performs similar analysis to ADDM by does not use AWR snapshots, rather it uses ASH data from SGA.
- Real-Time ADDM using in-memory real time performance data.
- Real-Time ADDM analysis is automatic when problem is detected.
- RT ADDM scans every 3 seconds using MMON process.
- RT ADDM does not use lock or latch.
- Things that would trigger RT ADDM analysis:
- High load – active session > 3x number of CPU
- I/O bound – I/O of active sessions concentrated on a single block read.
- CPU bound – Active sessions > 10% of all sessions and CPU > 50% utilization.
- Over-allocated memory – memory allocated > 95% of physical memory.
- Interconnect bound – Single block continually used.
- Session limit – near 100%
- Process limit – near 100%
- Hung session – hung session > 10% of all sessions.
- Deadlock detected – Any deadlock.
- MMON slave process will store ADDM reports created by AWR, which is accessible by DBA_HIST_REPORTS view.
- RT ADDM controls level analysis resource usage by:
- Duration between reports – RT ADDM will not produce new report if it has been less than 5 min since last report.
- Oracle RAC control – Only one RAC instance can create ADDM report at any given time.
- Repeated Triggers – A unique issue can only trigger an analysis if the impact is 100% or greater previous impact within 45 min.
- Newly identified issues – If new issue is identified, an analysis will be performed regardless of active session load.