How to create a on-demand AWR snapshot?

Using dbms_workload_repository.create_snapshot() one can create AWR snapshot.

Example: Creates the snapshot and returns the snap id. If ‘ALL’ is not passed it defaults to typical (statistics_level).

SQL> select dbms_workload_repository.create_snapshot('ALL') from dual;

DBMS_WORKLOAD_REPOSITORY.CREATE_SNAPSHOT()
——————————————
856

1 row selected.

How to generate AWR report?

There are few scripts that can be used to generate AWR HTML or text reports.
@?/rdbms/admin/awrrpt.sql – It is an interactive script that can be used to generate HTML or text reports. The script prompts for type of report requested and prompts for number of days of snapshots to choose from so based on that it displays snap ids to choose the start and end snapshot it.

…
796 27 Sep 2009 17:00 1
797 27 Sep 2009 18:00 1
798 27 Sep 2009 19:00 1
799 27 Sep 2009 20:00 1
800 27 Sep 2009 21:00 1

Specify the Begin and End Snapshot Ids
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Enter value for begin_snap: 795
Begin Snapshot Id specified: 795

Enter value for end_snap: 800
End Snapshot Id specified: 800

Specify the Report Name
~~~~~~~~~~~~~~~~~~~~~~~
The default report file name is awrrpt_1_795_800.html. To use this name,
press to continue, otherwise enter an alternative.
..

Another way of generating a report is one can query dba_hist_snapshot to find the snap id for the interval you are looking for.

SQL> column begin_interval_time format a25
SQL> column end_interval_time format a25
SQL> SELECT dbid, snap_id, begin_interval_time, end_interval_time from dba_hist_snapshot order by begin_interval_time;
DBID SNAP_ID BEGIN_INTERVAL_TIME END_INTERVAL_TIME
———- ———- ————————- ————————-
…
1992878807 798 27-SEP-09 06.00.13.120 PM 27-SEP-09 07.00.14.116 PM
1992878807 799 27-SEP-09 07.00.14.116 PM 27-SEP-09 08.00.15.051 PM
1992878807 800 27-SEP-09 08.00.15.051 PM 27-SEP-09 09.00.16.049 PM

SQL> SELECT output FROM TABLE (dbms_workload_repository.awr_report_text(1992878807, 1, 799, 800));

OUTPUT
——————————————————————————–
WORKLOAD REPOSITORY report for

DB Name DB Id Instance Inst Num Release RAC Host
———— ———– ———— ——– ———– — ————
TEST 1992878807 TEST 1 10.2.0.1.0 NO localhost.lo

Snap Id Snap Time Sessions Curs/Sess
——— ——————- ——– ———
Begin Snap: 799 27-Sep-09 20:00:15 15 2.0
End Snap: 800 27-Sep-09 21:00:16 15 2.0
…..
user_dump_dest /u01/oradata/admin/TEST/udump
————————————————————-

OUTPUT
——————————————————————————–

End of Report

@?/rdbms/admin/awrrpti.sql – Script can be used for the specified database and instance so the script in addition will prompt for dbid and instance number.
@?/rdbms/admin/awrddrpt.sql – Script can be used to generate a combine report of 2 different snapshots for comparison of performance in one report so it will prompt for two pairs of snapshot snapshots to compare against.
@?/rdbms/admin/awrinfo.sql – Script print AWR information like space usage by AWR, subset of AWR snap ids, Automatic Database Diagnostic Monitor (ADDM), Active Session History (ASH) information.

How to change AWR retention, interval,topnsql?

Using dbms_workload_repository.modify_snapshot_settings one can modify retention, interval and topnsql.

– get the dbid which is needed to passs to dbms_workload_repository.modify_snapshot_settings
SQL> select dbid from v$database;

DBID
———-
1992878807

– retention=>value in minutes so (45 days * 24 (hours per day) * 60 minutes per hour = 64800), max value can be set by passing a value of 0 which means forever
– internal=>60min (snap at this interval), a value of 0 will turn off AWR
SQL> exec dbms_workload_repository.modify_snapshot_settings(retention=>64800, interval=>60, topnsql=>100, dbid=>1992878807);

PL/SQL procedure successfully completed.

– shows retention and interval after it was modified
SQL> select extract( day from snap_interval) *24*60+extract( hour from snap_interval) *60+extract( minute from snap_interval ) snapshot_interval,
extract( day from retention) *24*60+extract( hour from retention) *60+extract( minute from retention ) retention_interval,
topnsql
from dba_hist_wr_control;

Snapshot Interval Retention Interval topnsql
—————– —————— ———-
60 64800 100

How to find AWR snapshot interval and retention settings?

Using this SQL one can find the snapshot interval and snapshot retention.

SQL> SELECT extract(day from snap_interval) *24*60+extract(hour from snap_interval) *60+extract(minute from snap_interval) snapshot_Interval,
extract(day from retention) *24*60+extract(hour from retention) *60+extract(minute from retention) retention_Interval
FROM dba_hist_wr_control;

Snapshot_Interval Retention_Interval
—————– ——————
60 10080