PH41756: IMPROVING LATCH CONTENTION IN DB2 Z/OS

Obtain the fix for this APAR.

APAR status

• Closed as new function.

Error description

• Improving latch contention in Db2 z/OS
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED:                                              *
  * All Db2 for z/OS users.                                      *
  ****************************************************************
  * PROBLEM DESCRIPTION:                                         *
  * Information in DSNV491I and DSNV523I                         *
  * was difficult to understand due to                           *
  * the fields not being labelled and                            *
  * certain identifying information such                         *
  * as the latch holder's thread token                           *
  * not being included.                                          *
  * In addition, certain latches may be                          *
  * held for too long before they are                            *
  * boosted, which may cause a buildup of                        *
  * contention on the latch and slow down                        *
  * processes on the system.                                     *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  When a latch holder's priority is boosted due to a long wait
  time, the DSNV522I message is issued. This message indicates
  the start of a summary of the 10 oldest waiters that resulted
  in the boost. For each of the waiters, a DSNV523I message is
  issued. The DSNV523I message displays information about the
  agents that caused the priority of a latch holder to be
  boosted, followed by Lines V490 and V491. Line V491 contains
  the same information as DSNV491I, which is issued by console
  command. Both messages lack labelling for the fields and other
  important information that could be used to diangose problems.
  Full monitoring is done every 60 seconds in which delayed
  latch waiters are scanned for and if their elapsed wait time
  exceeds a certain amount, the respective holders of the latch
  are boosted. The interval of 60 seconds per scan is sometimes
  too long if there is a lot of contention between threads.
  

Problem conclusion

Temporary fix

Comments

• DSNV491I and DSNV523I were modified to include labels for
  each field. The boosted agent's thread token and ACE address
  were also added to help aid in problem diagnosis.
  The initial latch boost is now done after waiting for more
  than 30 seconds instead of 60 seconds or half of the original
  IRLM timeout, whichever value is higher. Subsequent boosts
  for the same  agent will still remain at the greater of 60
  seconds or the IRLM timeout.
  ×**** PE23/12/27 FIX IN ERROR. SEE APAR PH58941  FOR DESCRIPTION
  

APAR Information

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

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

  UI92639 UI92640

Modules/Macros

• DSNVDTAD DSNVDTA  DSNVMON  DSNVDTID DSNFVDIR DSNVDRR  DSNVDTT
  DSNVDTP  DSNVDTQ  DSNFCDIR DSNLDTI2 DSNVDT   DSNVDTM  DSNVDTTD
  DSNVDTI
  

Fix information

• Fixed component name

  DB2 OS/390 & Z/

• Fixed component ID

  5740XYR00

Applicable component levels

• RC10 PSY UI92639

     UP23/07/15 P F307

• RD10 PSY UI92640

     UP23/07/15 P F307

Fix is available

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