PI69073: PREFETCH DISABLED DUE TO UNAVAILABILITY OF READ ENGINE

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• Prefetch engines were scheduled but not actually resumed.
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: DB2 users.                                   *
  ****************************************************************
  * PROBLEM DESCRIPTION: Prefetch engines becoming unusable      *
  *                      (neither scheduled nor on the free      *
  *                      chain) due to a cancel window.  If the  *
  *                      cancel window is hit often enough, and  *
  *                      most or all of the possible 600 engines *
  *                      are lost, prefetch requests will fail   *
  *                      with "no read engine available" (buffer *
  *                      pool statistic QBSTREE).                *
  *                                                              *
  *                      ABEND04E RC00C200A4 in DSNB5RAP.        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  In the process of scheduling a prefetch engine, there is a short
  interval where the engine has been taken off of the free chain
  but not yet resumed.  A latch is acquired in that window, so a
  wait on the latch provides a large cancel opportunity, where
  the engine is effectively lost.
  
  A timing window exists in which a prefetch is invalidly
  scheduled for a pageset being physically closed, which may
  result in an ABEND04E RC00C200A4 in DSNB5RAP and/or ABEND0C4 in
  various DSNB* CSECTs.
  

Problem conclusion

• The prefetch scheduling logic has been modified to acquire the
  latch outside of the deque/resume window.
  
  Additionally, the prefetch scheduling and physical close logic
  has been modified to prevent any prefetch being scheduled for
  an object being physically closed.
  

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:

  UI41949 UI41950

Modules/Macros

• DSNB1CPF DSNB1CPP DSNB1IOR DSNB1SPF
  

Fix information

• Fixed component name

  DB2 OS/390 & Z/

• Fixed component ID

  5740XYR00

Applicable component levels

• RA10 PSY UI41949

     UP16/11/08 P F611

• RB10 PSY UI41950

     UP16/11/08 P F611

Fix is available

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