OCP 12C – Resource Manager and Performance Enhancements


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Cyrille Modiano

OCP Oracle DBA in Montreal at DBSoft

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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.

Resource Manager

  • 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:
  2. Create the directive for the PDB
  3. Validate the pending area:
  4. Submit the 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:

 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.

Resource Manager

  • 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 :

  •  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.

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