IV47558: DIRECT I/O NOT ENABLED WHEN WRITING TO RECOVERY LOGS ON WEBSPHERE MQ FOR LINUX

WebSphere MQ V7.5 Fix Pack 7.5.0.3
Fix Pack 7.1.0.5 for WebSphere MQ V7.1

APAR status

• Closed as program error.

Error description

• WebSphere MQ on Linux does not use direct I/O when writing to
  the recovery log. The expected default behavior is that direct
  I/O is used. An 'strace' of strmqm should show two opens per log
  file, one using the O_DIRECT flag, rather than a single open.
  
  For example
  23342 open("/var/mqm/log/active/S0000000.LOG",O_RDWR|O_DSYNC)=8
  23342 open("/var/mqm/log/active/S0000000.LOG",
  O_RDWR|O_DSYNC|O_DIRECT) = 9
  

Local fix

• Direct I/O can be explicitly enabled with the following tuning
  parameter in the qm.ini as follows:
       TuningParameters:
         NoLogBuffering=TRUE
  

Problem summary

• ****************************************************************
  USERS AFFECTED:
  This issue affects users of IBM MQ on Linux platforms.
  
  Users who have deployed MQ using a log filesystem which does not
  tolerate the use of O_DIRECT should follow the guidance below to
  disable this optimization.
  
  
  
  
  Platforms affected:
  Linux (s390x),Linux (x86),Linux (x86-64)
  
  ****************************************************************
  PROBLEM SUMMARY:
  The intention of the code design was to use the O_DIRECT flag
  when opening recovery log files on Linux platforms.  The wrong
  constant was used when testing for the Linux platform and so the
  option was not enabled.
  

Problem conclusion

• The constant was corrected so that Linux platforms would use the
  O_DIRECT flag by default when opening recovery log files.
  
  This change in behavior can be overridden by adding the
  following to the relevant qm.ini file:
  
  TuningParameters:
  NoLogBuffering=FALSE
  
  Setting this tuning parameter will cause MQ to revert to the
  old behavior.
  
  ---------------------------------------------------------------
  The fix is targeted for delivery in the following PTFs:
  
  Version    Maintenance Level
  v7.1       7.1.0.5
  v7.5       7.5.0.3
  
  The latest available maintenance can be obtained from
  'WebSphere MQ Recommended Fixes'
  http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006037
  
  If the maintenance level is not yet available information on
  its planned availability can be found in 'WebSphere MQ
  Planned Maintenance Release Dates'
  http://www-1.ibm.com/support/docview.wss?rs=171&uid=swg27006309
  ---------------------------------------------------------------
  

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:

Fix information

• Fixed component name

  WMQ LIN X86 V7

• Fixed component ID

  5724H7224

Applicable component levels

• R710 PSY

     UP