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Oracle Resource Manager Enhancements in Oracle Database 12c Release 1 (12.1)

This article describes the enhancements to automatic consumer group switching in Oracle 12c Release 1 (12.1).

oracle 12cconfigurationintermediate
by OracleDba
14 views
1

Runaway Query Management - Automatic Consumer Group Switching

Managing runaway queries using automatic consumer group switching in resource manager has a long history. Oracle 12c introduces a number of changes related to consumer group switching. The parameter can now also be set to , so the trigger for a potential switch is logged, but no actual consumer group switch is performed. Plan directives can now include the and parameters to trigger a consumer group switch, so the current list of parameters for the procedure is now as follows. - : , , , , . - : Time in CPU seconds that will trigger a switch. - : When set to TRUE, Oracle estimates the elapsed time and if necessary switches the consumer group before the execution begins. - : The total size of I/O requests that will trigger a switch. - : The number of physical I/O requests that will trigger a switch. - : When set to TRUE, the switch is based on each top-level call. Once the call is complete, the consumer groups are switched back to original settings. When set to FALSE the switch is at session level and the new consumer group will remain until the session ends. - : The number of logical I/O requests that will trigger a switch. - : The elapsed time that will trigger a switch. The allowable values of the parameter are described below. - : Automatic consumer group switching is not enabled for this plan directive. - : The consumer group the session/call should be switched to if a threshold is reached. - : If a threshold is reached, the current call is cancelled, but the session is not killed. - : If a threshold is reached, the current session is killed. - : If a threshold is reached, the event is logged in SQL Monitor, but nothing happens to the call or session. For all the switch-related parameters, there is an equivalent parameter for altering the values using the procedure. Here is an example of automatic consumer group switching to cancel a SQL statement. We create a test user. In the following example we have a resource plan with a consumer group called for normal sessions. Any sessions with the consumer group that have a single call using CPU for more than 60 seconds will have that SQL cancelled. We allow the user to switch to the NORMAL_CG consumer group, then we set the initial consumer group for the user to . Finally we activate the plan. We can monitor the current consumer group assignment with the following query. Leave this session open so we can monitor the progress. In a separate session we connect to the test user, create a function that just sits on CPU for the specified number of minutes, then query the function. Back in our privileged session we see the initial consumer group. After approximately 60 seconds the query calling the BURN_CPU function has been cancelled. We clean up the example by disabling the plan, then deleting it.

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CONN sys/SysPassword1@//localhost:1521/pdb1 AS SYSDBA

--DROP USER testuser1 CASCADE;
CREATE USER testuser1 IDENTIFIED BY testuser1 QUOTA UNLIMITED ON users;
GRANT CREATE SESSION, CREATE PROCEDURE TO testuser1;

BEGIN
  DBMS_RESOURCE_MANAGER.clear_pending_area;
  DBMS_RESOURCE_MANAGER.create_pending_area;

  -- Create plan
  DBMS_RESOURCE_MANAGER.create_plan(
    plan    => 'long_running_query_plan',
    comment => 'Plan to handle long running queries.');

  -- Create consumer groups
  DBMS_RESOURCE_MANAGER.create_consumer_group(
    consumer_group => 'normal_cg',
    comment        => 'Consumer group for normal sessions.');

  -- Assign consumer groups to plan and define priorities
  DBMS_RESOURCE_MANAGER.create_plan_directive (
    plan                 => 'long_running_query_plan',
    group_or_subplan     => 'normal_cg',
    comment              => 'Normal Priority',
    mgmt_p1              => 100,
    switch_group         => 'CANCEL_SQL',
    switch_time          => 60,
    switch_for_call      => TRUE);

  DBMS_RESOURCE_MANAGER.create_plan_directive(
    plan             => 'long_running_query_plan',
    group_or_subplan => 'OTHER_GROUPS',
    comment          => 'Default',
    mgmt_p2          => 100);

  DBMS_RESOURCE_MANAGER.validate_pending_area;
  DBMS_RESOURCE_MANAGER.submit_pending_area;
END;
/

BEGIN
  DBMS_RESOURCE_MANAGER_PRIVS.grant_switch_consumer_group(
    grantee_name   => 'testuser1',
    consumer_group => 'normal_cg',
    grant_option   => FALSE);

  DBMS_RESOURCE_MANAGER.set_initial_consumer_group('testuser1', 'normal_cg');
END;
/

ALTER SYSTEM SET RESOURCE_MANAGER_PLAN = 'long_running_query_plan';

COLUMN username FORMAT A30
COLUMN resource_consumer_group FORMAT A30

SELECT username, resource_consumer_group
FROM   v$session
WHERE  username = 'TESTUSER1';

CONN testuser1/testuser1@//localhost:1521/pdb1

CREATE OR REPLACE FUNCTION burn_cpu (p_mins IN NUMBER)
  RETURN NUMBER
AS
  l_start_time DATE;
  l_number     NUMBER := 1;
BEGIN
  l_start_time := SYSDATE;
  LOOP
    EXIT WHEN SYSDATE - l_start_time > (p_mins/24/60);
    l_number := l_number + 1;
  END LOOP;
  RETURN 0;
END;
/

SELECT burn_cpu (5) FROM dual;

COLUMN username FORMAT A30
COLUMN resource_consumer_group FORMAT A30

SELECT username, resource_consumer_group
FROM   v$session
WHERE  username = 'TESTUSER1';

USERNAME                       RESOURCE_CONSUMER_GROUP
------------------------------ ------------------------------
TESTUSER1                      NORMAL_CG

SQL>

SQL> SELECT burn_cpu (5) FROM dual;

Error starting at line : 1 in command -
SELECT burn_cpu (5) FROM dual
Error report -
ORA-00040: active time limit exceeded - call aborted

SQL>

ALTER SYSTEM SET RESOURCE_MANAGER_PLAN = '';

BEGIN
  DBMS_RESOURCE_MANAGER.clear_pending_area;
  DBMS_RESOURCE_MANAGER.create_pending_area;

  DBMS_RESOURCE_MANAGER.delete_plan_cascade(
    plan    => 'long_running_query_plan');

  DBMS_RESOURCE_MANAGER.validate_pending_area;
  DBMS_RESOURCE_MANAGER.submit_pending_area;
END;
/
2

V$SQL_MONITOR

The V$SQL_MONITOR view includes four new resource manager columns. - : , , , - : , , , , - : The time of the last resource manager action. - : The current consumer group.
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Resource Manager with Container Databases (CDB) and Pluggable Databases (PDB)

In a multitennent environment resource manager performs two separate tasks. At the CDB level it controls the resources allocated to each PDB, allowing you to prioritise some PDBs over others. At the PDB level it controls the resources allocated to each session connected to the PDB, allowing you to prioritise some sessions over others, just as it does in pre-12c instances. For more information see: Hope this helps. Regards Tim...

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