How can you detect the cause of the degraded performance?

You notice that the performance of your production 24/7 Oracle 12c database has
significantly degraded. Sometimes you are not able to connect to the instance because it
hangs. You do not want to restart the database instance.
How can you detect the cause of the degraded performance?

A.
Enable Memory Access Mode, which reads performance data from SGA.

B.
Use emergency monitoring to fetch data directly from SGA for analysis.

C.
Run Automatic Database Diagnostic Monitor (ADDM) to fetch information from the latest
Automatic Workload Repository (AWR) snapshots.

D.
Use Active Session History (ASH) data and hang analysis in regular performance
monitoring,

E.
Run ADDM in diagnostic mode.

Explanation:
* In most cases, ADDM output should be the first place that a DBA looks when notified of a
performance problem.
* Performance degradation of the database occurs when your database was performing
optimally in the past, such as 6 months ago, but has gradually degraded to a point where it
becomes noticeable to the users. The Automatic Workload Repository (AWR) Compare
Periods report enables you to compare database performance between two periods of time.
While an AWR report shows AWR data between two snapshots (or two points in time), the
AWR Compare Periods report shows the difference between two periods (or two AWR
reports with a total of four snapshots). Using the AWR Compare Periods report helps you to
identify detailed performance attributes and configuration settings that differ between two
time periods.

Reference:
Resolving Performance Degradation Over Time