AWR_NEW

Automatic Workload Repository (AWR) in Oracle

Automatic Workload Repository

AWR is very similar to the STATSPACK as well as AWR is a replacement for

the STATSPACK utility.(AWR collects and stores database statistics relating to

problem detection and tuning ).

AWR generates performance data, such as system and session statistics,

Object-usage statistics , time-model statistics , high-load statistics, query

statistics and finally stores it in the SYSAUX tablespace.

When we create an Oracle database, AWR is automatically installed and

enabled. GATHER_STATS_JOB, to collect AWR statistics. This job is

created, and enabled automatically when creating a new Oracle 10g

database.

AWR is to collect database statistics (by default every hour) and this data is

maintained for a week and then purged. GATHER_STATS_JOB, to collect AWR

statistics every 1 hour. By default, the report will be for the last three days of

information.

AWR consists of ( Temporary , Persistent ) components.

1) Temporary : Memory statistics (Collection of statistics in the SGA) accessible

through V$dynamic views. 2) Persistent : Performance data in the form of

regular AWR Snapshots , access via (data dictionary views).

AWR scripts are found $ORACLE_HOME/rdbms/admin directory. The MMON

process is responsible for collecting the statistics in SGA and saving them to

the SYSAUX TABLESPACES.

EXPLORING AWR by THIYAGU GUNASEKARAN Page 1 of 22


When an instance is shutdown between 2 snapshots , AWR returns error.

Disable and Enable the Schedule Job

>>To disable this job using dbms_scheduler.disable >>

SQL> Exec dbms_scheduler.disable(’GATHER_STATS_JOB’);

>> To enable this job using the dbms_scheduler.enable >>

SQL> Exec dbms_scheduler.enable(’GATHER_STATS_JOB’);

AWR Setup

ALL

BASIC

TYPICAL

Basic disables AWR.

Typical activates standard level of collection (default option).

All same as typical & includes execution plans , timing info from OS.

STATISTICS_LEVEL (Parameter)

** Parameter statistics_level maintaining one of the three levels in AWR. **

>> Default value of statistics_level parameter >>

SQL> show parameter statistics_level;

NAME TYPE VALUE

statistics_level string TYPICAL

>> TO change statistics_level parameter to all >>

SQL>alter system set statistics_level = all;



** statistics_level = basic , also not recommended to use **

AWR is used to collect Performance Statistics

SQL Statistics.

Time Model Statistics

Operating System statistics

Database Object usage statistics.

Wait Statistics -- used to identify performance problems.

ASH statistics from V$ACTIVE_SESSION_HISTRORY

System & Session statistics from the V$SYSSTAT and V$SESSTAT.

ASH statistics, representing the history of recent sessions activity.

Object statistics determine both access & usage statistics of database

segments.

Time model statistics based on time usage for activities i.e. indicating the

amount of DB time associated with a process from V$SESS_TIME_MODEL

& V$SYS_TIME_MODEL views.

SQL statements are producing the highest load on the system, based on

elapsed time and CPU time .

AWR collects statistics from following V$views :

v$sysstat using for system stats.

v$sesstat using for session stats.

v$osstat using for operating system stats (avg_busy_ticks, avg_idle_ticks, etc)

v$service_stats wait statistics ( db cpu, app wait time, user commits, etc)



v$sys_time_model , v$sess_time_model Time model stats(DB time, java

execution time , pl/sql execution time , etc)

Database Performance stats

** Fall into one of three categories * *

Metrics

Sampled data

Cumulative values

** This topic discuss later on Database Statistics **

AWR Related useful Views :

DBA_HIST_WR_CONTROL AWR SettingsDBA_HIST_SNAPSHOT AWR Snapshot infoDBA_HIST_BASELINE AWR Baseline infoDBA_HIST_ACTIVE_SESS_HISTORY ASH info , Contents of active sessionDBA_HIST_SQL_PLAN SQL Execution plansDBA_HIST_DATABASE_INSTANCE Database Environment infoV$METRIC Metric infoV$METRICNAME Metrics associated with each groupV$METRICGROUP All Metric GroupV$METRIC_HISTORY Historical MetricsV$ACTIVE_SESSION_HISTORY (ASH) Sampled Every Second

dba_hist_sysstat (System statistics)

dba_hist_waitstat (Wait statistics)

dba_hist_sqlstat (SQL statistics)

dba_hist_sql_summary (Summary & Higher level SQL statistics)

dba_hist_sql_workarea



dba_hist_filestatxs (Datafile statistics)

dba_hist_sql_workarea_histogram

SNAP SHOTS

Snapshots are sets of historical data for specific time periods. By default

snapshots are taken every 60 mins. Data in the snapshot interval is analyzed

by Automatic Database Diagnostic Monitor (ADDM).

We can use DBMS_WORKLOAD_REPOSITORY procedures to manually create,

drop, and modify the snapshots but must be granted the DBA role.

Each snapshot has a unique ID know as "SNAP_ID". AWR compares snapshots

to determine , which SQL statements to capture based on the effect on the

system load.

DBMS_WORKLOAD_REPOSITORY Package to create or remove snapshots.

DBMS_WORKLOAD_REPOSITORY.CREATE_SNAPSHOT procedure creates a

manual snapshot in the AWR.

BASE LINE

A baseline is “ Pair of Snapshots ” , difference between two

snapshots.

In AWR, baselines are identified by range of snapshots preserved for

comparison. Baselines are can be used to compare performance against

similar periods in the past.

Baseline data gathered should include

Application statistics (transaction volumes, response time)



Database statistics

Operating system statistics

Disk I/O statistics

Network statistics

Create a Snapshot

SQL>exec dbms_workload_repository.create_snapshot;

Create a Baseline

SQL>exec dbms_workload_repository.create_baseline(start_snap_id => 1240 ,

end_snap_id=>1244 , baseline_name =>’latest’);

Delete Snapshots

SQL>exec dbms_workload_repository.drop_snapshot_range (low_snap_id =>

1077, high_snap_id => 1078);

Delete a Baseline

SQL>exec dbms_workload_repository.drop_baseline(baseline_name=> 'latest’

,cascade => FALSE);

================================================================

SQL>exec dbms_workload_repository.drop_baseline(baseline_name=> 'latest’

,cascade => TRUE);



Cascade Options

If cascade is TRUE, it will drop the snapshot in the baseline.

If cascade is FALSE, it will drop the baseline (not the snapshot).

>> Displaying list of Snapshots >>

SQL> select snap_id , snap_level , to_char(begin_interval_time,

' dd/mm/yy hh24:mi:ss ') begin from dba_hist_snapshot order by 1;

>> Check Snapshot Interval & Retention Period >>

SQL> select DBID, SNAP_INTERVAL , RETENTION from dba_hist_wr_control;

DBID SNAP_INTERVAL RETENTION

2092200073 +00000 01:00:00.0 +00007 00:00:00.0

/*Now I am going to change SNAP INTERVAL DURATION & RETENTION */

** Snap Interval duration : From 1 hour 15 MINS

** Retention : From 7days 1day

** Retention period (10080 mins =7days) ( 1440 mins = 1day ) **

SQL>exec dbms_workload_repository.modify_snapshot_settings(interval=>15,

retention=>1440);

PL/SQL procedure successfully completed.

>> Check Snapshot Interval & Retention Period after changed >>

SQL> select SNAP_INTERVAL , RETENTION from dba_hist_wr_control;

SNAP_INTERVAL RETENTION



+00000 00:15:00.0 +00001 00:00:00.0

Snapshot Interval – Snapshot are captured.

Snapshots , Baselines are “sets of historical data for a specific timeperiod “

used for performance comparison.

Producing AWR report

To run an AWR report, a user must be granted the DBA role. awrrpt.sql &

awrrpti.sql. Both SQL script generates an HTML or text report that displays

statistics for a range of snapshot Ids.

awrrpt.sql & awrrpti.sql are exactly same .

awrrpti report allows specific instance to report.

awrrpti.sql asks to enter dbid for particular instance.

SQL>@$ORACLE_HOME/rdbms/admin/awrrpt.sql

SQL>@$ORACLE_HOME/rdbms/admin/awrrpti.sql

The scripts prompt to enter

Report format (html or text),

Start snapshot_ id,

End snapshot_ id

Report filename.

Points to Remember:

awrrpt.sql



The awrrpt.sql SQL script generates an HTML or text report that displays

statistics for a range of snapshot Ids. Report went to $oracle_home\db_1\bin.

Begin and End Snapshot Id : Choose from the list displayed

Report Name: If leave blank , then it will take default file name.

awrrpti.sql

The awrrpti.sql script generates an HTML or text report , that displays

statistics for range of snapshot IDs on specified DATABASE & INSTANCE.

AWR report for different instances in a RAC database cluster. While running

the second script it asks the instance ID to generate the AWR report.

Example for to generate AWRRPT (awrrpt.sql)

SQL>@$ORACLE_HOME/rdbms/admin/awrrpt.sql

First , need to specify whether you want an HTML or a text report.

Enter value for report_type: text

Specify the number of days for which you want to list snapshot Ids.

Enter value for num_days: 3 (is default)

After the list displays, prompted for the beginning and ending snapshot Id

for the workload repository report.

Enter value for begin_snap: 1095

Enter value for end_snap: 1097

Next, accept the default report name or enter a report name. The default

name is accepted in the following example:

Enter value for report_name:

Using the report name awrrpt_1_95_97



The workload repository report is generated.

** If u need specific report name , enter report name “ XXXXXX “ **

** HTML format is much easier to read/navigate. **

** HTML format is highly recommended to use this for the output type. **

awrddrpt.sql

The awrddrpt.sql SQL script generates an HTML or text report that compares

detailed performance attributes and configuration settings between two

selected time periods.

awrsqrpt.sql

The awrsqrpt.sql SQL script generates an HTML or text report that displays

statistics of a particular SQL statement for a range of snapshot Ids. Run this

report to inspect or debug the performance of a SQL statement.

awrsqrpi.sql

The awrsqrpi.sql SQL script generates an HTML or text report that displays

statistics of a particular SQL statement for a range of snapshot Ids on a

specified database and instance. Run this report to inspect or debug the

performance of a SQL statement on a specific database and instance.

awrddrpi.sql

The awrddrpi.sql SQL script generates an HTML or text report that compares

detailed performance attributes and configuration settings between two

selected time periods on a specific database and instance.



addmrpt.sql

Automatic Database Diagnostic Monitor (ADDM) analyzes the AWR data on a

regular basis, then locates the root causes of performance problems, provides

recommendations for correcting any problems, and identifies non-problem

areas of the system . ADDM can be used to analyze performance issues often

saving time and resources reproducing a problem.

ashrpt.sql

Active Session History (ASH) is a very important feature to analyze sessions in

Oracle to troubleshoot transient problems . ASH information is stored within a

circular buffer in the SGA . ASH used to identify blocker and waiter identities

and their associated transaction identifiers and SQL for a specified duration.

Extract the AWR data

To extract AWR data at the SQL prompt

SQL> @$ORACLE_HOME/rdbms/admin/awrextr.sql

awrextr.sql script extracts the AWR data for a range of snapshots from the

database into a Data Pump export file.

Once created, this dump file can be transported to another system where the

extracted data can be loaded. To run the awrextr.sql script, need to be

connected to the database as the SYS user.

LOAD the AWR data

To load AWR data at the SQL prompt

SQL> @$ORACLE_HOME/rdbms/admin/awrload.sql



Once the export dump file is transported to the target system, can load the

extracted AWR data using the awrload.sql script.

awrload.sql script will first create a staging schema where the snapshot data is

transferred from the Data Pump file into the database.

The data is then transferred from the staging schema into the appropriate

AWR tables. To run the awrload.sql script, need to be connected to the

database as the SYS user.

SOME POINTS TO NOTE : -

awrrpt.sql statistics for a range of snapshot Ids.

AWR can be called from $ORACLE_HOME/rdbms/admin.

AWR outputs based on the events , between 2 snapshots.

awrsqrpt.sql statistics of a particular SQL statement for a range of snapshot

IDs to inspect performance of a SQL statement.

AWR is done through Enterprise Manager ,or DBMS_WORKLOAD_REPOSITORY

package. MODIFY_SNAPSHOT_SETTINGS procedure of this package can be

used to change the default snapshot settings.

Oracle kernel allocates a small distinct portion of the SGA to buffers , that

are dedicated to holding session history and other AWR related information.

** In-memory buffer is updated by MMNL and MMON processes **

Collection process involves from the SGA and their transfer to the physical

tables located in the workload repository.

AWR contains Two types of internal tablesEXPLORING AWR by THIYAGU GUNASEKARAN Page 12 of

22


AWR is stored in tables owned by ‘SYS’ but physically located on the SYSAUX

tablespace. Participate

Metadata Tables (WRM$_*) ,

Historical Statistics Tables (WRH$_*)

Metadata Tables:

These are used to control, process, and describe the Workload Repository

tables. For example, Oracle uses the metadata tables to determine when to

perform snapshots, and what to capture to disk.

Historical Statistics Tables:

These tables store historical statistical information about the database in the

form of snapshots. Each snapshot is a capture of the in–memory database

statistics data at a certain point in time.

AWR Performance Tables

AWR table names is prefixed with (wr)

wrm$ (Metadata tables),

wrh$ (History tables),

wri$ (Advisory tables).

wrm$ tables store metadata information for the Workload Repository.

The wrh$ tables store historical data or snapshots.

The wri$ tables: These 49 tables store data related to advisory functions.

DOES AWR capture all the SQL which was running in database ??

No



How to check whether SQL query captured in AWR ??

Concurrently "n" no of queries issued ... Can't . . . Hundreds, even thousands

of queries might have come-and-gone between snapshots. Even at snapshot

time, I know of no way to get "missed" SQL statements. . . .

Oracle provide a easy method to find out whether sql query captured or not

dbms_workload_repository.awr_sql_report_text

>> This ONLY show what WAS captured , not what was lost ! >>

SQL> select * from table (dbms_workload_repository.awr_sql_report_text

(&v_db_id, &v_inst_num, :b_snap_id, :e_snap_id, '&v_sql_id'));

Query has SQL* Plus ambersand variables & HOST variables so try like this

SQL>SELECT * FROM TABLE(dbms_workload_repository.awr_sql_report_text

(1692970157, 1, 1230, 1231, 'a01hp0psv0rrh'));

MMON captured only top resource consumed queries based on

dbms_workload_repository.modify_snapshot_settings arguments.

** (see dbms_workload_repository.modify_snapshot_settings chapter) **

DBMS_WORKLOAD_REPOSITORY



DBMS_WORKLOAD_REPOSITORY is a PLSQL package allows the DBA to

manage the AWR.

DBMS_WORKLOAD_REPOSITORY package lets to perform operations such as

managing snapshots and baselines.

DBMS_WORKLOAD_REPOSITORY .MODIFY_SNAPSHOT_SETTINGS procedure is

used to configure snapshot intervals & AWR data retention in the database.

Default value of the snapshot interval is 60 minutes, and the default setting for

retention is 10,080 minutes which is seven days.

SQL> desc dbms_workload_repository

PROCEDURE CREATE_BASELINE

PROCEDURE DROP_BASELINE

PROCEDURE CREATE_SNAPSHOT

PROCEDURE DROP_SNAPSHOT_RANGE

PROCEDURE MODIFY_SNAPSHOT_SETTINGS

** Desc dbms_workload_repository for additional information **

DBMS_WORKLOAD_REPOSITORY.MODIFY_SNAPSHOT_SETTINGS

This procedure controls two aspects of snapshot generation.

INTERVAL setting how often snapshots are automatically captured.

RETENTION setting how long snapshots are retained in the Workload

Repository.

SYNTAX



DBMS_WORKLOAD_REPOSITORY.MODIFY_SNAPSHOT_SETTINGS ( retention IN NUMBER DEFAULT NULL, interval IN NUMBER DEFAULT NULL, topnsql IN NUMBER DEFAULT NULL, dbid IN NUMBER DEFAULT NULL);

RETENTION time in mins.

Retention setting affects how long snapshots are to keep in the Workload

Repository. Specified Retention value must be in the range of MIN_RETENTION

(1day) to MAX_RETENTION (100 years).

INTERVAL

Interval setting between each snapshot (unit of mins).

Interval setting affects how often snapshots are automatically captured.

Specified value must be in the range MIN_INTERVAL (10 minutes) to

MAX_INTERVAL (1 year)

DBID

Database Identifier in AWR for which to modify the snapshot settings. If null

specified , the local dbid will be used.

TOPNSQL

Topnsql is used to specify the number of SQL to collect for each criteria like

elapsed time, CPU time, parse calls, shareable memory, version count etc ..

Topnsql is normally set to a small number like 10, can see the most current

SQL statements. This SQL information is normally purged after a period of time.

MMON captured top SQL based on below criteria.



SQL> exec

dbms_workload_repository.modify_snapshot_settings(topnsql => 30);

>> No of SQL statements captured depends on statistics_level setting >>

If set statistics_level =all, AWR will collect the top 100 SQL statements for

each of the criteria so , total of 1400 SQL statements per snapshot. 14*100

=1400

If set statistics_level=typical, AWR will collect the Top-30 SQL statements for

each SQL category a total of 420 per snapshot. (default leval). 30*14=420.

There are 14 criteria in an AWR report & AWR will capture the top-n-SQL

for each of following criteria :-

14 Criteria in AWR:-

1. Elapsed Time (ms)

2. CPU Time (ms)

3. Executions

4. Buffer Gets

5. Disk Reads

6. Parse Calls

7. Rows

8. User I/O Wait Time (ms)

9. Cluster Wait Time (ms)

10. Application Wait Time (ms)

11. Concurrency Wait Time (ms)



12. Invalidations

13. Version Count

14. Sharable Mem(KB)

Note : ORA-13530:

SQL> exec dbms_workload_repository.modify_snapshot_settings(topnsql=>10);

invalid TOPNSQL 10, must be in the range (30, 50000)

View the Repository Tables

SQL> select table_name from dba_tables where tablespace_name = ‘SYSAUX’

and substr(table_name, 1,2) = ‘WR’ and rownum <= 20 order by 1;

FINAL TIPS : -

Set the retention to 60 or 90 days.

Review the reports at least once a week

Look into ASH also for more information

Watch the size of the SYSAUX Tablespace.

Don't change the snapshot interval, It is a good balance between

too often and too few.

All DBA_HIST views are confusing , Look at these general categories:

File statistics

SQL statistics

Undo Statistics

Segment Statistics

Recovery Statistics



Time-model statistics

Concurrency statistics

Instance tuning statistics

General System statistics

Points to keep in mind :-

V$STATISTICS_LEVEL view displays information about the status of the

statistics or advisories controlled by the STATISTICS_LEVEL parameter.

IF STATISTICS_LEVEL =ALL, additional statistics are added to the set of statistics

collected with the TYPICAL setting. They are Timed OS statistics and plan

execution statistics.

Oracle captures every SQL ?

ABSOLUTELY NO. Capturing every SQL might be too heavy. Oracle only

captures part of the SQLs which are considered to be meaingful workloads.

Actual configuration is controlled by following procedure.

dbms_workload_repository.modify_snapshot_settings.

Important AWR Tables

DBA_HIST_SNAPSHOT

PKSNAP_ID

DBID, INSTANCE_NUMBER

BEGIN_INTERVAL_TIME

END_INTERVAL_TIME



DBA_HIST_SQLSTAT

PK

SNAP_ID

SQL_ID, PLAN_HASH_VALUE (DBID, INSTANCE_NUMBER)

BASIC STATS

Executions, Gets, Reads

TIME

CPU, Elapsed

WAIT TIME:

IO, Concurrency, App

Time in microseconds

DBA_HIST_SYSSTAT

PK

SNAP_ID

STAT_ID (DBID, INSTANCE_NUMBER)

AWR snapshots of V$SYSSTAT

Includes STAT_NAME (almost 400!)

Does NOT include deltas, you need to calculate these yourself

Watch out for stat counter resets (bounces)

“DB time” in units of centiseconds

Use as basis of comparison

DBA_HIST_SQLTEXT

PK

SQL_ID



DBID

No SNAP_ID, INSTANCE_NUMBER

Preserves SQL_TEXT even when found nowhere else

DBA_HIST_SYSTEM_EVENT

PK

SNAP_ID

EVENT_ID (DBID, INSTANCE_NUMBER)

AWR snapshots of V$SYSTEM_EVENT

Includes EVENT_NAME (almost 900!)

Does NOT equal sum of ASH sampling

Time is clearly in units of microseconds

DBA_HIST_SEG_STAT_OBJ

PK

OBJ#, DATAOBJ# (DBID)

Object details (name, owner, type, tablespace)

Several segment types:

Table, Table Partition

Index, Index Partition , LOB

Performance Tuning Questions

1. How to tune a SQL Queries ?

2. What is a driving table in a SQL query ?

3. How do you keep the store PLSQL blocks in memory.

4. How would you begin to troubleshoot an ORA-3113 error?



5. How to get Statspack reports and what you will look into main events

6. You’re getting high “busy buffer waits” – how to find what’s causing it?

7. A User/Developer calls in saying that their process is running very slow

How would you go about troubleshooting the issue?

8. An automatic job running via DBMS_JOB has failed. Knowing only that

“it’s failed”, how do you approach troubleshooting this issue?

9. Database is hung. Old and new user connections alike hang on impact.

What do you do? Your SYS SQLPLUS session IS able to connect ?

10.What would you use to improve performance on an insert statement

that places millions of rows into that table?

11.You’re running a DML statement and you get an error saying the rollback

segment cannot extend. how do to fix this ?


Documents

AWR_NEW