Automatic Workload Repository (AWR)

Automatic Workload Repository (AWR)

The AWR collects and stores database statistics relating to problem detection and tuning. AWR is a replacement for the statspack utility which helps gather database performance statistics. AWR generates snapshots of key performance data, such as system and session statistics, segment-usage statistics, time-model statistics, high-load statistics and stores it in the sysaux tablespace.
AWR provides statistics in two formats

• temporary - in memory collection of statistics in the SGA, accessible via the V$ views
• persistent - type of performance data in the form of regular AWR snapshots which you access via the DBA_ views

The MMON process is responsible for collecting the statistics in the SGA and saving them to the sysaux tablespaces.
AWR will collect data on the following

• Base statistics that are also part of the v$SYSSTAT and V$SESSTAT views
• SQL statistics
• Database object-usage statistics
• Time-model statistics
• Wait statistics
• ASH (active session history) statistics
• Operating system statistics

Tables that AWR uses to collect statistics
v$sys_time_model	time model stats (db time, java execution time, pl/sql execution time, etc)
v$osstat	operating system stats (avg_busy_ticks, avg_idle_ticks, etc)
v$service_stats	wait statistics ( db cpu, app wait time, user commits, etc)
v$sysstat	system stats
v$sesstat	session stats

Database performance stats fall into one of three categories:

• Cumulative values - collect stats over a period of time from the v$sysstat, etc
• Metrics - use the collected stats to make some sort of sense.
• Sampled data - the ASH sampler is used to collect these stats.

AWR Setup
To active the AWR change the system parameter statistics_level to one of three values

• basic - this option disables the AWR
• typical (default) - activates standard level of collection
• all - same as typical but includes execution plans and timing info from the O/S

Active	alter system set statistics_level = typical; alter system set statistics_level = all;
De-active	alter system set statistics_level = basic;
Display	show parameter statistics_level;

To change the snapshot interval and how many days the snapshots are kept you use the package dbms_workload_repository or Enterprise Manager

Snapshot configuration
Change snapshotting values	exec dbms_workload_repository.modify_snapshot_settings ( interval => 60, retention => 43200); interval = minutes retention = seconds
Display values	select * from dba_hist_wr_control;
Snapshot Management
Create a snapshot	exec dbms_workload_repository.create_snapshot;
Delete snapshots	exec dbms_workload_repository.drop_snapshot_range (low_snap_id => 1077, high_snap_id => 1078);
Create a baseline	exec dbms_workload_repository.create_baseline (start_snap_id => 1070, end_snap_id => 1078, baseline_name => 'Normal Baseline');
Delete a baseline	exec dbms_workload_repository.drop_baseline (baseline_name => 'Normal Baseline', cascade => FALSE);
Display snapshots	select snap_id, begin_interval_time, end_interval_time from dba_hist_snapshot order by 1;
View the repository tables	select table_name from dba_tables where tablespace_name = ‘SYSAUX’ and substr(table_name, 1,2) = ‘WR’ and rownum <= 20 order by 1;
Useful Views
dba_hist_active_sess_history	ASH info (see below)
dba_hist_baseline	baseline info
dba_hist_database_instance	environment data
dba_hist_sql_plan	sql execution path data
dba_hist_wr_control	AWR settings
dba_hist_snapshot	snapshot info in the AWR

AWR Report
To run AWR report you can use the following operating system scripts or use Enterprise Manager.

awrrpt.sql	the script will ask for begin snapshot and end snapshot and will be generated in text format Note: reports went in $oracle_home\db_1\bin
awrrpti.sql	the script will ask for begin snapshot and end snapshot and will be generated in HTML format Note: reports went in $oracle_home\db_1\bin

You can obtain more information regarding the AWR from automatic database diagnostic manager (ADDM).