It stores these snapshots in the Automatic Workload Repository (AWR) for problem detection and self-tuning purposes. You can use these snapshots to monitor and diagnose the database performance for a specific time period.

AWR compares the difference between snapshots to determine which SQL statements to capture based on the effect on the system load. This reduces the number of SQL statements that must be captured over time. After the snapshots are created, Automatic Database Diagnostic Monitor (ADDM) processes the data in the snapshots for performance analysis and resolution.

By default, Oracle Database automatically collects snapshots every hour and retains the statistics in AWR for eight days. However, you can use the AWR Settings option on the Performance Hub page and manually configure some settings for snapshot collection, such as:

• Enable and disable snapshot collection for the database.

• Set the interval for snapshots.

  A snapshot interval determines the frequency at which snapshots are captured. A smaller interval means higher frequency, which increases the volume of data collected by AWR.

• Specify the number of days to store the snapshots in AWR.

  A retention period determines how long the statistical data is maintained before it gets deleted permanently. A longer retention period takes more space in AWR.