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Oracle Tips by Burleson |
How to Use the AWR
To get started with the AWR, nothing needs
to be installed other than the Oracle10g database. This is one
feature of the AWR that is a benefit over STATSPACK. The AWR
automatically collects data as soon as Oracle10g is installed and
running. With STATSPACK, the DBA determined the frequency of data
collection and then scheduled a job to run at the appropriate
interval to gather data. With the AWR, the documentation states
that these collections are done every 30 minutes, but the frequency
can be modified by the user. The resulting data is stored in the
AWR for seven days, by default, after which the data is
automatically purged.
Based on user testing, it appears that the
default of 30 minute snapshot intervals, as stated by the
documentation, may not be correct. In some cases, the interval
appeared to be 60 minutes rather than 30 minutes. A later section
will provide a method for determining the actual “default” sampling
interval. Additionally, instructions on how to change these
defaults are also included. Every DBA should assess the frequency
of the snapshots as well as the length of time they are retained and
adjust the AWR settings accordingly.
This data is gathered and populated into the
AWR by the new 10g MMON and MMNL (MMON Lite) processes. MMON is
also responsible for issuing alerts when there are metrics that
exceed thresholds.
As far as using this data, this book will
only address the use of scripts to access the AWR data. Oracle
Enterprise Manager (OEM) can also be used to access the data, but
OEM is a topic unto itself. In this book, this topic is limited to
the non-gui tools or direct access to the data dictionary objects.
Since nothing extra needs to be installed,
the data tables that support this feature are up for discussion.
The AWR contains a number of new tables in the data dictionary.
These are:
The structure of
dba_hist_active_sess_history is essentially the same as
v$active_session_history with the exception of the additional fields
at the top with which to track the snapshot details for when and
where the data was collected. This view actually represents the
data that is periodically collected from v$active_session_history in
a manner similar to the way STATSPACK collects data.
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 |
