Pickleball spielen

This article contains a complete working example for the Resource Manager on the command line for those of you who can’t use the Enterprise Manager fort it. Believe me, I feel your pain 😉

As a good practice, PL/SQL procedures should be using DBMS_APPLICATION_INFO to mark their modules and actions. Not only for monitoring purpose but also to provide a way to tweak the system if things start going ugly in terms of performance. Here’s where the Resource Manager steps in.

Sessions can be assigned to different consumer groups depending on the module. Say we have an application with certain modules that sometimes consume an awful lot of CPU resources or way too much parallel processes. When the problem surfaces, you may not have enough time to fix the coding because it’s a live production run. The mentioned tweak – if prepared beforehand – may save the day. Let’s look at an example:

 
BEGIN
  DBMS_RESOURCE_MANAGER.CREATE_PENDING_AREA();

  DBMS_RESOURCE_MANAGER.SET_CONSUMER_GROUP_MAPPING_PRI(
    EXPLICIT => 1,
    SERVICE_MODULE_ACTION => 2,
    SERVICE_MODULE => 3,
    MODULE_NAME_ACTION => 4,
    MODULE_NAME => 5,
    SERVICE_NAME => 6,
    ORACLE_USER => 7,
    CLIENT_PROGRAM => 8,
    CLIENT_OS_USER => 9,
    CLIENT_MACHINE => 10,
    CLIENT_ID => 11);

  DBMS_RESOURCE_MANAGER.VALIDATE_PENDING_AREA();
  DBMS_RESOURCE_MANAGER.SUBMIT_PENDING_AREA();
  DBMS_RESOURCE_MANAGER.CLEAR_PENDING_AREA();
END;
/

The above set the priority of MODULE_NAME over ORACLE_USER, which is not the default. The state of the priorities can be seen in DBA_RSRC_MAPPING_PRIORITY. Now I create two consumer groups:

BEGIN
  DBMS_RESOURCE_MANAGER.CREATE_PENDING_AREA();

  DBMS_RESOURCE_MANAGER.CREATE_CONSUMER_GROUP (
     CONSUMER_GROUP => 'A_GROUP',
     COMMENT        => 'A Group');

  DBMS_RESOURCE_MANAGER.CREATE_CONSUMER_GROUP (
     CONSUMER_GROUP => 'B_GROUP',
     COMMENT        => 'B Group');

  DBMS_RESOURCE_MANAGER.VALIDATE_PENDING_AREA();
  DBMS_RESOURCE_MANAGER.SUBMIT_PENDING_AREA();
  DBMS_RESOURCE_MANAGER.CLEAR_PENDING_AREA();
END;
/

My demo user ADAM gets the right to be a member of these consumer groups:

BEGIN
  DBMS_RESOURCE_MANAGER.CREATE_PENDING_AREA();

  DBMS_RESOURCE_MANAGER_PRIVS.GRANT_SWITCH_CONSUMER_GROUP (
   GRANTEE_NAME   => 'ADAM',
   CONSUMER_GROUP => 'A_GROUP',
   GRANT_OPTION   =>  FALSE);

  DBMS_RESOURCE_MANAGER_PRIVS.GRANT_SWITCH_CONSUMER_GROUP (
   GRANTEE_NAME   => 'ADAM',
   CONSUMER_GROUP => 'B_GROUP',
   GRANT_OPTION   =>  FALSE);

  DBMS_RESOURCE_MANAGER.VALIDATE_PENDING_AREA();
  DBMS_RESOURCE_MANAGER.SUBMIT_PENDING_AREA();
  DBMS_RESOURCE_MANAGER.CLEAR_PENDING_AREA();
END;
/

Now the part where consumer group and module is combined respectively mapped:

BEGIN
  DBMS_RESOURCE_MANAGER.CREATE_PENDING_AREA();

  DBMS_RESOURCE_MANAGER.SET_CONSUMER_GROUP_MAPPING
     (DBMS_RESOURCE_MANAGER.MODULE_NAME, 'A_MODULE', 'A_GROUP');

  DBMS_RESOURCE_MANAGER.SET_CONSUMER_GROUP_MAPPING
     (DBMS_RESOURCE_MANAGER.MODULE_NAME, 'B_MODULE', 'B_GROUP');

  DBMS_RESOURCE_MANAGER.VALIDATE_PENDING_AREA();
  DBMS_RESOURCE_MANAGER.SUBMIT_PENDING_AREA();
  DBMS_RESOURCE_MANAGER.CLEAR_PENDING_AREA();
END;
/

Next comes the Resource Manager Plan. The restrictions are a bit rigid to show an obvious effect – 95 to 5 percent favors Group A very much over Group B:

BEGIN
  DBMS_RESOURCE_MANAGER.CREATE_PENDING_AREA();

  DBMS_RESOURCE_MANAGER.CREATE_PLAN(
     PLAN    => 'TESTPLAN',
     COMMENT => 'test');

  DBMS_RESOURCE_MANAGER.CREATE_PLAN_DIRECTIVE (
     PLAN                     => 'MYPLAN', 
     GROUP_OR_SUBPLAN         => 'SYS_GROUP',    /* built-in group */
     COMMENT                  => 'SYS Group',
     MGMT_P1                  => 100);

  DBMS_RESOURCE_MANAGER.CREATE_PLAN_DIRECTIVE (
     PLAN                     => 'MYPLAN', 
     GROUP_OR_SUBPLAN         => 'A_GROUP',
     COMMENT                  => 'A GROUP',
     parallel_degree_limit_p1 => 8 ,          /* RESTRICTION HERE */
     MGMT_P2                  => 95);

  DBMS_RESOURCE_MANAGER.CREATE_PLAN_DIRECTIVE (
     PLAN                     => 'MYPLAN', 
     GROUP_OR_SUBPLAN         => 'B_GROUP',
     COMMENT                  => 'B GROUP',
      parallel_degree_limit_p1 => 2 ,          /* RESTRICTION HERE */
      MGMT_P2                  => 5);

  DBMS_RESOURCE_MANAGER.CREATE_PLAN_DIRECTIVE (
     PLAN                     => 'MYPLAN', 
     GROUP_OR_SUBPLAN         => 'OTHER_GROUPS', /* built-in group */
     COMMENT                  => 'Others',
     MGMT_P3                  => 100);

  DBMS_RESOURCE_MANAGER.VALIDATE_PENDING_AREA();
  DBMS_RESOURCE_MANAGER.SUBMIT_PENDING_AREA();
  DBMS_RESOURCE_MANAGER.CLEAR_PENDING_AREA();

END;
/

So far, no restriction is in place, because the plan is not yet active. But everything is now prepared. Should Module B consume too much CPU or demand too much parallel processes, the plan can be set with this :

BEGIN
    DBMS_RESOURCE_MANAGER.SWITCH_PLAN(plan_name => 'MYPLAN');
END;
/

The sessions that have the module set are subject to the restrictions as soon as the plan is activated. If a new module is set during an existing session, the session is switched into the new consumer group. The parallel restriction have precedence over parallel hints:

SQL> connect adam/adam@prima
Connected.
SQL> select distinct sid from v$mystat;

       SID
----------
	 4

SQL> exec dbms_application_info.set_module(module_name => 'A_MODULE',action_name => 'A-ACTION')

PL/SQL procedure successfully completed.

SQL> select resource_consumer_group from v$session where sid=4;

RESOURCE_CONSUMER_GROUP
--------------------------------
A_GROUP

SQL> select /*+ parallel (dual,16) */ * from dual;

D
-
X

SQL> select * from v$pq_sesstat; 

STATISTIC		       LAST_QUERY SESSION_TOTAL     CON_ID
------------------------------ ---------- ------------- ----------
Queries Parallelized			1	      1 	 0
DML Parallelized			0	      0 	 0
DDL Parallelized			0	      0 	 0
DFO Trees				1	      1 	 0
Server Threads				8	      0 	 0
Allocation Height			8	      0 	 0
Allocation Width			1	      0 	 0
Local Msgs Sent 		       24	     24 	 0
Distr Msgs Sent 			0	      0 	 0
Local Msgs Recv'd		       22	     22 	 0
Distr Msgs Recv'd			0	      0 	 0
DOP					8	      0 	 0
Slave Sets				1	      0 	 0

13 rows selected.

SQL> exec dbms_application_info.set_module(module_name => 'B_MODULE',action_name => 'B-ACTION')

PL/SQL procedure successfully completed.

SQL> select resource_consumer_group from v$session where sid=4;

RESOURCE_CONSUMER_GROUP
--------------------------------
B_GROUP

SQL> select /*+ parallel (dual,16) */ * from dual;

D
-
X

SQL> select * from v$pq_sesstat; 

STATISTIC		       LAST_QUERY SESSION_TOTAL     CON_ID
------------------------------ ---------- ------------- ----------
Queries Parallelized			1	      2 	 0
DML Parallelized			0	      0 	 0
DDL Parallelized			0	      0 	 0
DFO Trees				1	      2 	 0
Server Threads				2	      0 	 0
Allocation Height			2	      0 	 0
Allocation Width			1	      0 	 0
Local Msgs Sent 			8	     32 	 0
Distr Msgs Sent 			0	      0 	 0
Local Msgs Recv'd			8	     30 	 0
Distr Msgs Recv'd			0	      0 	 0
DOP					2	      0 	 0
Slave Sets				1	      0 	 0

13 rows selected.

To test the CPU restrictions, I used scripts like this:

set serveroutput on
declare
    v_starttime timestamp;
    v_endtime timestamp;
begin
    dbms_application_info.set_module(module_name => 'A_MODULE',action_name => 'A-ACTION');
    v_starttime:=current_timestamp;
    for i in 1..1000000000 loop
        for j in 1..1000000000 loop
            for k in 1..10000 loop
                null;
            end loop;
        end loop;
    end loop;
    v_endtime:=current_timestamp;
    dbms_output.put_line('Seconds elapsed Module A: '||to_char(extract(second from v_endtime-v_starttime)));
end;
/

With CPU_COUNT set to 1 (remember this is a dynamic parameter since 11g and this Instance Caging feature requires a Resource Manager plan to be active), two sessions each running scripts like that one setting module A and the other module B are enough to see the effect. On my system, both sessions need about 15 seconds without the plan while module A completes in about 10 seconds vs module B in 20 seconds with the plan active.

Apart from the shown restrictions, there are other useful options available like Active Session Pool, Maximum Estimated Execution Time, Undo Quota and Idle Blocker Time. Each of these can come in handy to tweak or troubleshoot a misbehaving application without having to touch the code. See here for a whole lot of more details.

The demo was done with 12c but works the same in 11g, probably also in 10g. As always: Don’t believe it, test it! 🙂