In the Real-Time: Last Hour mode, the data in the Performance Hub is sourced from Active Session History (ASH). The ASH data is written to disk when the ASH buffer is filled up or after 1 hour, and is stored as part of the AWR framework.
By default, AWR has a retention period of 8 days. When you view historical data in the Performance Hub, you are viewing statistics collected as part of the hourly snapshots in AWR.
You use the Select Time Period field in the Performance Hub to determine the time periods for which statistics are available for viewing. Because Oracle Database statistics are stored in memory for one hour, the Real Time - Last Hour option always appears in the Select Time Period list.
The historical data options that are available in the Select Time Period list change, depending on the time period for which data is available in AWR, as shown in the following table:
| Time Period for Which AWR Data is Available | Historical Options in the Select Time Period List |
|---|---|
|
Less than 24 hours |
Historical - All |
|
More than 24 hours, but less than 7 days |
Historical - Day Historical - All1 Historical - Custom |
|
7 days |
Historical - Day Historical - Week Historical - Custom |
|
8 days or more2 |
Historical - Day Historical - Week Historical - Custom |
After you choose a historical option from the Select Time Period field, you use the time picker to specify the time period for which data is displayed in the Performance Hub tabs.
The following table describes the data displayed and available for selection in the time picker when different values are selected in the Select Time Period field for the Performance Hub:
| Selected Time Period | Time Picker | Description |
|---|---|---|
|
Real Time - Last Hour |
Displays statistics for the past hour from memory |
Data is displayed in 5 minute blocks in the time picker. Use the time picker to select from 1 minute to 60 minutes of data to display in the Performance Hub. |
|
Historical - Day |
Displays statistics from an hour up to 24 hours from AWR |
Data is displayed in 1 hour blocks in the time picker. Use the time picker to select from 1 hour to 24 hours of data to display in the Performance Hub. |
|
Historical - All |
Displays statistics for the length of time for which AWR statistics exist |
Appears only when less than one day's data or less than one week's data is available in AWR. The Historical - All option is available only when there is not enough AWR data to provide the Historical - Day option or the Historical - Week option. |
|
Historical - Week |
Displays statistics from a day up to 7 days from AWR |
Data is displayed in 1-day blocks in the time picker. Use the time picker to select from 1 day to 7 days of data to display in the Performance Hub. When Historical - Week is selected, the current week of AWR data appears in the time picker by default. To view AWR data from the previous week in the time picker, use the < button in the time picker. |
|
Historical - Custom |
Displays AWR statistics for the length of time you select in the Select Time Period dialog box after choosing the Historical - Custom option |
Use the time picker to select the time period for which you want to display statistics in the Performance Hub. |
See Also:
Oracle Database Concepts for more information about ASH
Oracle Database Performance Tuning Guide for more information about changing the default AWR retention period
This option is available only when less than one day's data or less than one week's data is available in AWR. Database statistics that are stored in memory are flushed to AWR after one hour.
The default AWR retention period is 8 days, so you must change the default AWR retention period to store more than a week of data in AWR