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Oracle Tips by Burleson 


A baseline is simply a snapshot at a point in time.  Database information can be compared against a baseline to determine if things have gotten better, worse, or stayed the same.  Baselines can be created with the dbms_workload_repository.create_baseline procedure.  Some DBAs might currently be experiencing DBA nirvana where all of the users are happy and engaged in DBA worship.  First, these DBAs should enjoy it while it lasts.  Secondly, these DBAs should create a baseline so when the users start throwing stones, data will be available for comparing the new performance metrics to the ones when things were good.  With any luck, those DBAs will find the cause of the problem and be quickly back on the road to happiness.  

For everyone but that lucky DBA, a baseline should be taken as soon as the system is stable.  For a typical Online Transaction Processing (OLTP) system, this stable time may fall on Monday at mid-day since users in earlier time zones have been at work for several hours and users in later time zones have not yet taken lunch.  On Mondays, many workloads will have a weekend backlog which means that the load will be somewhat higher than that for the rest of the week.  After analyzing this report and making changes which have been properly vetted through the TEST and DEVELOPMENT environments, an additional baseline can be taken at the same time on another Monday and a statistical analysis performed to determine what has changed, whether it is a good change and if the change is what had been expected.

After taking a baseline of a two-hour window of work from one day and another from the next day, the dba_hist_baseline will look something like Figure 9.6.  Notice that the baseline names in this example are simply the date of the baseline in yyyy-mm-dd order.  This makes sorting very easy using only the baseline_name field.  However, baseline name is merely a text field and a baseline called “fred and ginger dance partners” could just as easily be created.

The above book excerpt is from:

Oracle Wait Event Tuning

High Performance with Wait Event Iinterface Analysis 

ISBN 0-9745993-7-9  

Stephen Andert

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