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Oracle Tips by Burleson |
Baselines
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
http://www.rampant-books.com/book_2004_2_wait_tuning.htm |
