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Providing a new HPU parameter so that we can chose the number of BSAM buffers for SORTIN.

  • When unloading and sorting data due to ORDER BY option, HPU reads data from tablespace and write it to DFSORT SORTIN dataset via QSAM with BUFNO=60, that is a default.
  • In the environment where zHPF is enabled, DFSORT has used BSAM for SORTIN since z/OS V2.2. 
  • DFSMS builds BSAM buffers below the 16MB line based on its design.
  • If a previous PGM/process ready the DCB for input with specific BUFNO, DFSORT open the INPUT with that DCB. It means that BUFNO for the previous QSAM is passed to the subsequent BSAM.
  • If we use parallel unloading (Default: PARALLEL=20, MAXSORT=20), we're likely to run short of private storage below 16MB line and it can cause S878-10 abend. It's more likely to occur when migrating to z/OS V2.2 or higher.

 

For example:


27993 (BLKSIZE) * 60 (BUFNO) * 5 (Parallel) = 8,397,900 KB = 8.2 MB

=> If the maximum size of virtual private storage below 16MB line is 8 MB, a job must abnormally terminate with S878-10.

 

 

Refference:

 

1. DFSORT: Summary of Changes by Release

https://www-01.ibm.com/support/docview.wss?uid=isg3T7000084&aid=1

"A program that invokes DFSORT, ICETOOL or ICEGENER will now be able to exploit the High PerformanceFicon (zHPF) hardware. When zHPF is available, DFSORT SORT or MERGE applications will use BSAM forSORTIN, SORTOUT and OUTFIL data sets."

 

2. z/OS DFSMS Using Data Sets: Managing SAM Buffer Space

https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.2.0/com.ibm.zos.v2r2.idad400/bufaq.htm

"If the system builds the buffer pool for a BSAM user, the buffer pool resides below the 16 MB line."

 

3. DFSORT development comment in CSP Case #TS002838843

"I confirmed this to DFSORT development. He said DFSORT use all the information it is available at run time. So, if a previous PGM/process ready the DCB for input with specific BUFNO, DFSORT OPEN the INPUT with that DCB. As a result, buffer pool is obtained using provided blocksize and bufno.(if zHPF is enabled)"

  • Avatar32.5fb70cce7410889e661286fd7f1897de Guest
  • Nov 19 2019
  • Delivered
Who would benefit from this IDEA? HPU customers who enable zHPF.
How should it work?

We have to add a new parameter to HPU so that we can choose the number of BUFNO with BSAM access for SORTIN.

We have some workaround like below, but it's inconvenient because we cannot maximize parallel degree and zHPF advantage. It prevents us from getting performance benefit  especially for customers unloading tablespace having a considerable number of partitions.

 

Workaround:

  • Decrease HPU PARALLEL and MAXSORT parameter
  • Specify DEBUG $EXCPI$ with DFSPARM DD
Idea Priority Medium
Priority Justification It's expected that users with HPU, zHPF and z/OS V2.2 or higher will increase.
  • Attach files
  • Avatar40.8f183f721a2c86cd98fddbbe6dc46ec9
    Guest commented
    14 Oct 12:23am

    This new parameter is required for customer.

  • Avatar40.8f183f721a2c86cd98fddbbe6dc46ec9
    Guest commented
    13 Oct 01:39pm

    New parameters, QSAM-BUFFERS ( bufno_seq , bufno_sortin ) and BUFNO for SORTIN sequential QSAM (VUM038/QSSBUFNO) were provided by PH21188.

    UI69029 v5.1

    UI69013 v4.3

  • Avatar40.8f183f721a2c86cd98fddbbe6dc46ec9
    Guest commented
    21 Nov, 2019 07:10am

    I agree

  • Avatar40.8f183f721a2c86cd98fddbbe6dc46ec9
    Guest commented
    20 Nov, 2019 03:54am

    This request should be a mandatory matter in HPU.

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