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Specifying the Time Period for Which to Display Statistics

In the Real-Time: Last Hour modę, thc data in the Performance Hub is sourccd from Active Session History (ASH). The ASH data is writtcn to disk when thc ASH buffer is

fillcd up or after I hour, and is storcd 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 availabie for viewing. Bccause 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 availabie in AWR, as shown in the fol łowi ng table: