PH21188: ALLOW SPECIFIC SETTING OF BUFNO FOR SORTIN TO CIRCUMNVENT MEMORYOUTAGE CAUSED BY DFSORT WHEN ZHPF IS ENABLED

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• For some unloads (SELECT statement with ORDER clause processed
  in native mode or with SORT EXTERNAL option, unload from image
  copies requiring to be sorted), Db2 HPU invokes a sort program
  that can be the site default sort program (when SORTUTIL is set
  to SORT) or DB2 SORT (when SORTUTIL=DB2
  SORT).
  
  When the default sort program is invoked and Db2 HPU need to
  process several sort tasks in parallel (i.e. when parallelism is
  allowed with MAXSORT set to a value greater than 1), Db2 HPU
  launches several sort task taking the consumption of memory
  below the 16MB line into account as follows. It first launches
  sort tasks via E15 that require memory below the 16MB line and,
  when the remaining memory is supposed not to be enough to launch
  an E15 sort task (i.e. the remaining memory is less than the
  value set for LOWMEM), it launches sort tasks via SORTIN that do
  not require significant amount of memory below the 16 MB line.
  
  Potential issue when DFSORT is the default sort program and zHPF
  is enabled
  ----------------------
  Since z/OS V2.2 when zHPF is enabled, DFSORT uses BSAM for
  SORTIN which implies the use of memory below the 16 MB line and
  the amount of memory depends on the BUFNO parameter.
  
  Db2 HPU writes into the SORTIN data set using QSAM access with a
  BUFNO value as specified through the VUM022/QSBUFNO parmlib
  parameter. Unexpectedly, DFSORT uses/inherits this BUFNO value
  - meant for QSAM access - for accessing SORTIN in BSAM access.
  
  As the typical value for QSBUFNO is too big as a BUFNO parameter
   for BSAM, the fact that Db2 HPU launches SORTIN sort tasks - if
   DFSORT and zHPF are involved - can lead to a shortage of the
  private storage below 16MB line resulting in an ABENDS878-10.
  
  As VUM022/QSBUFNO drives the BUFNO value for any QSAM data set
  access, decreasing the value of VUM022/QSBUFNO is not a suitable
  solution as it would decrease the overall performance of Db2
  HPU.
  

Local fix

• When the above issue (ABENDS878-10) occurs, consider reducing
  the parallelism degree of the unload that applies to lds reading
   and table space. For example, set lower values for lds and ts
  in the PARALELLISM (lds,,ts) option.
  

Problem summary

• ****************************************************************
  * USERS AFFECTED: Users of Db2 High Performance Unload         *
  *                 for z/OS                                     *
  ****************************************************************
  * PROBLEM DESCRIPTION: For some unloads (SELECT statement with *
  *                      ORDER clause processed in native mode   *
  *                      or with SORT EXTERNAL option, unload    *
  *                      from image copies requiring to be       *
  *                      sorted), Db2 HPU invokes a sort program *
  *                      that can be the site default sort       *
  *                      program (when SORTUTIL is set to SORT)  *
  *                      or DB2 SORT (when SORTUTIL=DB2 SORT).   *
  *                                                              *
  *                      When the default sort program is        *
  *                      invoked and Db2 HPU need to process     *
  *                      several sort tasks in parallel (i.e.    *
  *                      when parallelism is allowed with        *
  *                      MAXSORT set to a value greater than 1), *
  *                      Db2 HPU launches several sort task      *
  *                      taking the consumption of memory below  *
  *                      the 16MB line into account as follows.  *
  *                      It first launches sort tasks via E15    *
  *                      that require memory below the 16MB line *
  *                      and, when the remaining memory is       *
  *                      supposed not to be enough to launch an  *
  *                      E15 sort task (i.e. the remaining       *
  *                      memory is less than the value set for   *
  *                      LOWMEM), it launches sort tasks via     *
  *                      SORTIN that do not require significant  *
  *                      amount of memory below the 16 MB line.  *
  *                                                              *
  *                      Potential issue when DFSORT is the      *
  *                      default sort program and zHPF is        *
  *                      enabled                                 *
  *                      ----------------------                  *
  *                      Since z/OS V2.2 when zHPF is enabled,   *
  *                      DFSORT uses BSAM for SORTIN which       *
  *                      implies the use of memory below the     *
  *                      16 MB line and the amount of memory     *
  *                      depends on the BUFNO parameter.         *
  *                                                              *
  *                      Db2 HPU writes into the SORTIN data set *
  *                      using QSAM access with a BUFNO value as *
  *                      specified through the VUM022/QSBUFNO    *
  *                      parmlib parameter. Unexpectedly, DFSORT *
  *                      uses/inherits this BUFNO value          *
  *                      - meant for QSAM access - for accessing *
  *                       SORTIN in BSAM access.                 *
  *                                                              *
  *                      As the typical value for QSBUFNO is too *
  *                      big as a BUFNO parameter for BSAM, the  *
  *                      fact that Db2 HPU launches SORTIN sort  *
  *                      tasks - if  DFSORT and zHPF are         *
  *                      involved - can lead to a shortage of    *
  *                      the private storage below 16MB line     *
  *                      resulting in an ABENDS878-10.           *
  *                                                              *
  *                      As VUM022/QSBUFNO drives the BUFNO      *
  *                      value for any QSAM data set access,     *
  *                      decreasing the value of VUM022/QSBUFNO  *
  *                      is not a suitable solution as it would  *
  *                      decrease the overall performance of Db2 *
  *                      HPU.                                    *
  ****************************************************************
  * RECOMMENDATION: Apply the PTF                                *
  ****************************************************************
  Allow specific setting of BUFNO for SORTIN to circumnvent memory
  outage caused by DFSORT when zHPF is enabled.
  

Problem conclusion

• Code has been changed to fix this problem
  

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:

Modules/Macros

• INZ$$PRM INZCHECK INZSGEN  INZTDSC  INZTPMEM INZTVAR  INZUTILK
  

Fix information

• Fixed component name

  DB2 HI PERF UNL

• Fixed component ID

  5697F4400

Applicable component levels

• R510 PSY UI69029

     UP20/04/22 P F004

Fix is available

• Select the PTF appropriate for your component level. You will be required to sign in. Distribution on physical media is not available in all countries.