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  Oracle Tips by Burleson

Easy Oracle Automation
Chapter 4 -
Automatic Workload Repository and Automatic Database Diagnostic Monitor

Base Statistics, Metrics, and Statistics Levels

BASIC is the computation of the AWR statistics with metrics turned off. TYPICAL is the default value and collects only part of the statistics. It represents what is typically needed for 10g administration. Setting the parameter to ALL will retain all the statistics.

A baseline is defined on a pair of snapshots to tag sets of data for important time periods. Each baseline is unique for one and only one pair of snapshots. A baseline is identified by a user created name or a system generated identifier. A baseline can be manually named by running the create_baseline procedure and by specifying a name and a pair of snapshot identifiers.

A baseline identifier is assigned to the newly created baseline, which is unique for the life of the database. Baselines are used to retain snapshot data for comparison with current system behavior and the set up of threshold based alerts.

The MMON process purges all older snapshots on a nightly basis to make room for new statistics. Snapshots are removed in chronological order. Snapshots pertaining to baselines are retained until the baselines are removed.  MMON tries to limit its purge task in the management window defined by the DBA. The amount of historical AWR statistics can be controlled by setting a retention period.

The above text is an excerpt from:

Easy Oracle Automation
Oracle10g Automatic Storage, Memory and Diagnostic Features

ISBN 0-9745993-6-0

by Dr. Arun Kumar R.

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