PM70270: A LOWER BUFFER HIT RATIO OR MORE SYNCHRONOUS I/O IF VPSEQT IS SET TO A SMALL VALUE

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• When a random Getpage buffer miss resulted in DB2 stealing a
  buffer from the sequential LRU chain, DB2 did not remove the
  buffer from the sequential LRU chain when it should.  This meant
  that random pages were more likely constricted by VPSEQT.
  Therefore in some cases, recently used buffers were stolen more
  quickly than less recently used buffers, resulting in a a lower
  buffer hit ratio or more synchronous I/O.   The impact of this
  problem is relatively small if the default VPSEQT value of 80%
  is used, but the impact is likely to be large if VPSEQT is set
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All DB2 users.                               *
  ****************************************************************
  * PROBLEM DESCRIPTION: A lower buffer pool hit ratio or more   *
  *                      synchronous I/O.                        *
  ****************************************************************
  * RECOMMENDATION:                                              *
  ****************************************************************
  When a random GetPage operation steals a buffer from the
  sequential LRU (SLRU) chain, DB2 does not reclassify the stolen
  buffer. In rare cases, it may result in a lower buffer pool hit
  ratio or more synchronous I/O.
  

Problem conclusion

• DB2 has been fixed to reclassify a buffer that is stolen from
  the SLRU chain for a random GetPage operation.
  

Temporary fix

• *********
  * HIPER *
  *********
  

Comments

APAR Information

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

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

  UK82555 UK82556

Modules/Macros

• DSNB1CMS DSNB1GET
  

Fix information

• Fixed component name

  DB2 OS/390 & Z/

• Fixed component ID

  5740XYR00

Applicable component levels

• RA10 PSY UK82555

     UP12/10/28 P F210

• R910 PSY UK82556

     UP12/10/28 P F210

Fix is available

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