To compare a baseline to another baseline:

1. On the Database Administration page, under Statistics Management, click Automatic Workload Repository.
The Automatic Workload Repository page appears.


2. Under Manage Snapshots and Preserved Snapshot Sets, click the link next to Preserved Snapshot Sets.
The Preserved Snapshot Sets page appears.


3. Select the baseline you want to use for the report. At least one existing preserved snapshot set must be available to be used as a baseline.
From the Actions list, select Compare Periods and click Go.
The Compare Periods: Second Period Start page appears. Under First Period, the selected baseline is displayed.


4. You can compare the baseline selected in the first period to another baseline or a pair of snapshots.
o To compare to another baseline, select Select a Preserved Snapshot Set and then the baseline you want to use in the second period.

o To compare to a pair of snapshots, select Select Beginning Snapshot and then the beginning snapshot you to use in the second period.
Click Next. The Compare Periods: Second Period End page appears. Continue with the next step.

5. Select the ending snapshot for the snapshot period that will be included in the report and click Next.

6.Review the selected periods that will be included in the report and click Finish.

7. To view the report, click the Report tab.



-Another way to perform the comparison, without using Em is using the functions provided.

We an generate the AWR differences report, passing in the DBID, Instance Number, Begin and End Snapshot IDs for the first period and then the second period.

select * from TABLE(DBMS_WORKLOAD_REPOSITORY.awr_diff_report_html(4034329550,1,8947,8951,
4034329550,1,8971,8975));


The report shows information for both periods, layed out for easy comparison.