Oracle have provided many performance gathering and reporting tools over the years. Originally the UTLBSTAT/UTLESTAT scripts were used to monitor performance metrics. Oracle8i introduced the Statspack functionality which Oracle9i extended. In Oracle 10g statspack has evolved into the Automatic Workload Repository (AWR).
The AWR is used to collect performance statistics including:
V$SESS_TIME_MODEL
and V$SYS_TIME_MODEL
views. V$ACTIVE_SESSION_HISTORY
view. V$SYSSTAT
and V$SESSTAT
views. The repository is a source of information for several other Oracle 10g features including:
By default snapshots of the relevant data are taken every hour and retained for 7 days. The default values for these settings can be altered using:
BEGIN DBMS_WORKLOAD_REPOSITORY.modify_snapshot_settings( retention => 43200, -- Minutes (= 30 Days). Current value retained if NULL. interval => 30); -- Minutes. Current value retained if NULL. END; /
The changes to the settings are reflected in the DBA_HIST_WR_CONTROL
view. Typically the retention period should capture at least one complete workload cycle. If you system has monthly archive and loads a 1 month retention time would be more beneficial that the default 7 days. An interval of "0" switches off snapshot collection, which in turn stops much of the self-tuning functionality, hence this is not recommended. Automatic collection is only possible if the STATISTICS_LEVEL
parameter is set to TYPICAL
or ALL
. If the value is set to BASIC
manual snapshots can be taken, but they will be missing some statistics.
Extra snapshots can be taken and existing snapshots can be removed using:
EXEC DBMS_WORKLOAD_REPOSITORY.create_snapshot; BEGIN DBMS_WORKLOAD_REPOSITORY.drop_snapshot_range ( low_snap_id => 22, high_snap_id => 32); END; /
Snapshot information can be queried from the DBA_HIST_SNAPSHOT
view.
A baseline is a pair of snapshots that represents a specific period of usage. Once baselines are defined they can be used to compare current performance against similar periods in the past. You may wish to create baseline to represent a period of batch processing like:
BEGIN DBMS_WORKLOAD_REPOSITORY.create_baseline ( start_snap_id => 210, end_snap_id => 220, baseline_name => 'batch baseline'); END; /
The pair of snapshots associated with a baseline are retained until the baseline is explicitly deleted:
BEGIN DBMS_WORKLOAD_REPOSITORY.drop_baseline ( baseline_name => 'batch baseline', cascade => FALSE); -- Deletes associated snapshots if TRUE. END; /
Baseline information can be queried from the DBA_HIST_BASELINE
view.
The following workload repository views are available:
V$ACTIVE_SESSION_HISTORY
- Displays the active session history (ASH) sampled every second. V$METRIC
- Displays metric information. V$METRICNAME
- Displays the metrics associated with each metric group. V$METRIC_HISTORY
- Displays historical metrics. V$METRICGROUP
- Displays all metrics groups. DBA_HIST_ACTIVE_SESS_HISTORY
- Displays the history contents of the active session history. DBA_HIST_BASELINE
- Displays baseline information. DBA_HIST_DATABASE_INSTANCE
- Displays database environment information. DBA_HIST_SNAPSHOT
- Displays snapshot information. DBA_HIST_SQL_PLAN
- Displays SQL execution plans. DBA_HIST_WR_CONTROL
- Displays AWR settings. Oracle provide two scripts to produce workload repository reports (awrrpt.sql and awrrpti.sql). They are similar in format to the statspack reports and give the option of HTML or plain text formats. The two reports give essential the same output but the awrrpti.sql allows you to select a single instance. The reports can be generated as follows:
@$ORACLE_HOME/rdbms/admin/awrrpt.sql @$ORACLE_HOME/rdbms/admin/awrrpti.sql
The scripts prompt you to enter the report format (html or text), the start snapshot id, the end snapshot id and the report filename. The resulting report can be opend in a browser or text editor accordingly.
The automated workload repository administration tasks have been included in Enterprise Manager. The "Automatic Workload Repository" page is accessed from the main page by clicking on the "Administration" link, then the "Workload Repository" link under the "Workload" section. The page allows you to modify AWR settings or manage snapshots without using the PL/SQL APIs.