Tools and Utilities - Expert Oracle RAC Performance Diagnostics and Tuning - page 154

Like AWR, ADDM can also be generated using EM or using the addmrpt.sql script available in the $ORACLE_HOME/
rdbms/admin/ directory. These reports are stored by default for 30 days in the database before being purged. Reports
are generated on predefined thresholds (which can be modified) for a predetermined set of areas. For example, the
user I/O is defined by the parameter DBIO_EXPECTED and defaults to 1000 milliseconds. Another parameter that is used
to calculate the amount of database time spent is the DB_ELAPSED_TIME parameter, which defaults to 0 milliseconds.
Both these parameters can be modified using the DBMS_ADVISOR.SET_DEFAULT_TASK_PARAMETER PL/SQL procedure.
ADDM can be accessed by selecting the Advisor Central from either of the following pages:

• Clustered Database Performance page

• Database Instance Performance page

Once ADDM is selected using either of the options, EM automatically generates an ADDM analysis report on the
latest AWR snapshot available and allows for regeneration of analysis based on a different snapshot period.
In Figure 6-11 ADDM provides an overall performance of the database and provides a list of findings based on
the analysis of the snapshots selected. Apart from providing the findings, the analysis also reports on the percentage
of impact. In this case, the impact is for Virtual Memory Paging and the percentage impact is 99.8%. The ADDM time
scale shows considerable wait times from 5:30 PM thru about 10 AM the next day. This is the timeframe for the batch
application execution.

Figure 6-11. ADDM database activity