PK21985: TIME SPENT IN LG_RETRY OR LG_FORCE WAITS IS LOTS LONGER THAN THE LGDFINT INTERVAL. THIS CAUSES TASK TO HAVE EXCESS JCIOWTT .

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Under certain conditions, tasks suspend in LG_DEFER or
  LG_FORCE waits for longer than the LGDFINT interval.  It happens
  like this:
  1- A group of tasks all get to a point where they need to force
      a write to DFHLOG.
  2- The data they need to write all gets batched together and the
      tasks suspend in LG_DEFER (the 1st task in the batch) and
      LG_FORCE (the rest of the tasks in the batch.)  CICS waits
      to do the IXGWRITE until the LGDFINT interval expires in
      hopes that more tasks' data might get added to the batch.
  3- But there are no more tasks doing anything.  The CICS
      dispatcher considers it safe to do an operating system wait
      since the last 8 operating system waits have been short.
  4- There is nothing to wake CICS out of the operating system
      wait except for a 1/4 second tick.  So tasks spend about
      250 ms in the LG_DEFER and LG_FORCE waits.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All.                                         *
  ****************************************************************
  * PROBLEM DESCRIPTION: Excessive journal wait times due to     *
  *                      large number of LG_DEFER suspends.      *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  CICS will drive LG_DEFER suspends to delay forced I/O requests
  to the system log and so allow other tasks to store their log
  data in the same log buffer before the I/O commences.  These
  LG_DEFER suspends are typically very short (the default is 5ms).
  However, it is possible for the CICS Dispatcher to drive
  partition exit processing and return control to MVS when such a
  suspend has begun.  Such a partition exit wait will suspend the
  CICS region for a longer period (unless it is posted by an
  external event, such as an I/O completing).  This can lead to
  LG_DEFER suspends taking considerable periods of time to
  complete.
  
  Additional keywords:
  DSGTCT                           DS TCB CPU Time
  DSGSYSW  MVS Waits               Op. System Waits
  DSGACT   Accum CPU Time / TCB    Total TCB CPU Time
  DSGTWT   Accum Time in MVS Wait  Op. System Wait Time
  DSGTDT   Accum Time Dispatched   Total TCB Dispatch Time
  

Problem conclusion

• DFHDSDS3 has been changed to reduce the number of times that a
  partition exit wait occurs.  Although it is not possible to
  completely eliminate partition exits, the average log defer
  interval value will now be much closer to the value specified by
  log manager's log defer interval value, LGDFINT.
  
  The CICS Transaction Server for z/OS Version 3 Release 1 CICS
  Supplementary Data Areas manual, LY33-6108-00, will be updated
  as follows:
  
  Add NO_LGDFINT_PE to the DFHDSANC control block (CICS Dispatcher
  Anchor Block) at offset (8C) as follows:
  
   (8C)   UNSIGNED        4     DS_FLAGS          flag strip
           1...  ....            POST_EXIT_
                                 ENABLED
           .1..  ....            NO_LGDFINT_PE
           ..1.  ....            *
  
  Add NO_PE_FINISH to the DFHDSANC control block at offset (798)
  as follows:
  
  (798)   CHARACTER       8     NO_PE_FINISH      No delay for
                                                  partition exit
                                                  if earlier
  
  The CICS Transaction Server for z/OS Version 3 Release 1 CICS
  System Definition Guide, SC34-6428-00, will be updated as
  follows:
  
  In the description of system initialization parameter LGDFINT in
  section "The system initialization parameter descriptions" in
  chapter "Specifying CICS system initialization parameters", add
  the following sentence at the end of the paragraph beginning
  "For CICS system with many tasks ...":
  
  "The actual interval may also be affected by the need for tasks
  to wait across a partition exit.".
  

Temporary fix

• FIX AVAILABLE BY PTF ONLY
  

Comments

APAR Information

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

  PK16311

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

  UK14697

Modules/Macros

•    DFHDSANC DFHDSDS3
  

Fix information

• Fixed component name

  CICSTS 3.1 Z/OS

• Fixed component ID

  5655M1500

Applicable component levels

• R400 PSY UK14697

     UP06/05/26 P F605

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.