Use Resource Manager for a CDB and a PDB

Managing Resources between PDBs

• The Resource Manager uses Shares ans Utilization limit to manage resources allocated to PDBs.
• The more “Shares” you allocate to a PDB, the more resource it will have.
• Shares are allocated through DBMS_RESOURCE_MANAGER.CREATE_CDB_PLAN_DIRECTIVE.
• One directive can only concern one PDB and you can’t have multiple directive for the same PDB in the same plan.

• You can limit resource utilization of a specific PDB by using the UTILIZATION_LIMIT of the CREATE_CDB_PLAN_DIRECTIVE procedure. UTILIZATION_LIMIT is expressed in percentage of total system resources, if you set it to 50 it, the PDB will be able to use 50% of total system resources (CPU, I/O, parallel server).
• The PARALLEL_SERVER_LIMIT parameter let you limit the parallel server utilization for a PDB.
• If you don’t define a plan for a PDB, the default one applies, by default a PDB is being allocated :
  • 1 Share
  • No Utilization Limit
  • No Parallel Server Utilization limit

Create a CDB Resource Plan

Here is the step by step to create a CDB resource plan:

1. Create a pending area:

   exec DBMS_RESOURCE_MANAGER.CREATE_PENDING_AREA();
   

2. Create the directive for the PDB

   BEGIN
     DBMS_RESOURCE_MANAGER.CREATE_CDB_PLAN_DIRECTIVE(
       plan                  => 'newcdb_plan', 
       pluggable_database    => 'operpdb', 
       shares                => 1, 
       utilization_limit     => 20,
       parallel_server_limit => 30);
   END;
   /
   

3. Validate the pending area:

   exec DBMS_RESOURCE_MANAGER.VALIDATE_PENDING_AREA();
   

4. Submit the pending area:

   exec DBMS_RESOURCE_MANAGER.SUBMIT_PENDING_AREA();

•  This plan will limit total  system resource utilization for operpdb to 20% and this same PDB can use 30% of total PARALLEL_SERVERS_TARGET . The shares is set to default value (1).
• To activate a plan:

SQL> alter system set resource_manager_plan='my_plan';

 Create a PDB Resource Plan

• It is also possible to create a Resource Manager plan at the PDB level.
• A PDB Resource Plan let you define how the portion of system resource sallocated by the CDB plan to your PDB will be used within this PDB.

• There are rules to create a Resource Manager plan in a PDB:
  • You can’t create a multi-level plan.
  • You are limited yo 8 consumer groups (the limit is 32 for non-cdb).
  • You can’t create subplans in a PDB plan.
• The method to create and manage a PDB resource plan is the same than a CDB, you just have to connect to the PDB before creating the plan.
• You can see all Resource Manager plan created for CDB and PDB by querying the V$RSRC_PLAN view

 Multiprocess Multithreaded Architecture

• Oracle 12c intoduces a new background processes architecture, some of the usual background processes will now run as threads within an OS process.
• This architecture change will (according to oracle) reduce memory and cpu usage and increase performance for parallel executions.
• To activate the new Multiprocess Multithreaded architecture you need to enable it explicitly, it is disabled by default :

SQL> alter system set threaded_execution=true scope=spfile;

•  When the “thread mode” is enable, you can’t use OS authentication, you need to use password authentication.
• To see which process run as thread and which one is a real os process you can query the v$process view. It contains a new column STID. If the STID is equal to the SPID, the process is a real OS process, if the STID is different from the SPID then it is a thread an the SPID indicates to which OS process the thread depends.

SELECT SPID, STID, PROGRAM FROM V$PROCESS ORDER BY SPID;

SPID   STID   PROGRAM
-----  -----  ---------------------------
7190   7190   oracle@samplehost (PMON) 
7192   7192   oracle@samplehost (PSP0) 
7194   7194   oracle@samplehost (VKTM) 
7198   7198   oracle@samplehost (SCMN) 
7198   7200   oracle@samplehost (GEN0) 
7202   7202   oracle@samplehost (SCMN) 
7202   7204   oracle@samplehost (DIAG) 
7198   7205   oracle@samplehost (DBRM) 
7202   7206   oracle@samplehost (DIA0)