PH34378: EXCESSIVE CPU UTILIZATION DURING HIGH CONCURRENT DBAT TRANSACTION PROCESSING

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• High CP CPU utilization observed being consumed
  by non-enclave, preemptible SRBs in the ssidDIST
  address space.
  
  
  The V11 apar is PH34080
  
  
  
  Additional Keywords and Symptoms:
  *********************************
  DB2 DB2DDF DB2HighPerfDBAT
  

Local fix

• no local workaround
  

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * All Db2 12 Distributed Data Facility (DDF)                   *
  * users.                                                       *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * Excessive CPU utilization by                                 *
  * preemptible SRBs within ssidDIST                             *
  * address space while not under an                             *
  * enclave.                                                     *
  ****************************************************************
  * RECOMMENDATION:                                              *
  * Apply corrective PTF when available                          *
  ****************************************************************
  Db2 creates a WLM enclave at the start of a client
  connection's request processing. The enclave is then
  associated with a WLM service class.  The WLM service class is
  chosen based on all the current client connection and request
  properties that exist at the time of the WLM enclave
  creation. This processing provides the ability to have each
  client transaction be processed under its own appropriate WLM
  goal. When the client application then commits or rolls back
  its transaction, the enclave is then deleted. To manage the
  creation of enclaves, MVS serializes enclave creations.  This
  serialization can result in each concurrent enclave creator,
  which are waiting for enclave creation to complete, to cycle
  waiting on a CPU.  Since the create enclave is performed by
  Db2 while running on a non-enclave, preemptible SRB in the
  ssidDIST address space, the CP CPU utilization charged to the
  ssidDIST address space will increase significantly as the
  number of concurrent DBATs needing an enclave increases.
  This increase in CPU utilization may also result in the
  increase in the number of CP CPUs utilized by the ssidDIST
  address space. The increase in the concurrency of DBATs
  creating enclaves, which results in the increased demand for
  CPU utilization, is observed primarily when running with high
  performance DBATs.
  

Problem conclusion

• Db2 12 high performance DBAT processing, activated by the Db2
  command:
   -MODIFY DDF PKGREL(BNDOPT|BNDPOOL)
  and any packages utilized by a DBAT that were bound with
  with RELEASE DEALLOCATE, has been changed as follows:
  - the WLM enclave, which was created to control the processing
    of the first transaction of the client connection, will no
    longer be deleted at the end of the transaction processing
  - the WLM enclave will be deleted when it is determined that
    the high performance DBAT has been used by its associated
    client connection for greater than 200 transactions, the
    high performance DBAT has not received a new processing
    request from its associated client connection within the
    POOLINAC amount of time (seconds), or, the DBAT associated
    with a client connection is being terminated when the client
    terminates the connection.
  - accounting trace records will still be generated for each of
    the, up to, 200 transactions (assuming no resources held
    past their commits)
  This change only affects high performance DBAT processing.
  
  ************************* ATTENTION ************************
  With this change, the effective response time of the enclave
  will be longer than the response time to process a single
  transaction when using high performance DBATs.
  It is highly recommended that the WLM service classes, used
  to manage the processing of the client's connection when
  using high performance DBATs, be changed to use velocity
  goals. Existing WLM service classes utilizing response time
  or percentile response time goals will generally not meet
  their performance objectives.
  ************************* ATTENTION ************************
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  UI74139

Modules/Macros

• DSNLQCTL
  

Fix information

• Fixed component name

  DB2 OS/390 & Z/

• Fixed component ID

  5740XYR00

Applicable component levels

• RC10 PSY UI74139

     UP21/02/26 P F102

Fix is available

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