IZ63035: -XSHARECLASSES SLOWDOWN ATTEMPTING TO LOAD CLASS

APAR status

• Closed as program error.

Error description

• Error Message: In rare situations, a thread can take many
  seconds to attempt to load a class when the shared classes
  feature is enabled.
  This normally only occurs when multiple threads are attempting
  to load the same class simultaneously, and the class does not
  exist (java.lang.ClassNotFoundException would eventually be
  thrown).
  .
  Stack Trace: The problem can be identified by observing a thread
  emitting the j9shr.48 tracepoint repeatedly, as in the example
  below:
  j9shr.48   Event       CM access: waiting for another JVM to
  load class - waited 1 times
  j9shr.48   Event       CM access: waiting for another JVM to
  load class - waited 2 times
  j9shr.48   Event       CM access: waiting for another JVM to
  load class - waited 3 times
  j9shr.48   Event       CM access: waiting for another JVM to
  load class - waited 4 times
  .
  

Local fix

• The problem can be avoided by adding the
  -Xshareclasses:noReduceStoreContention option.  This disables
  the shared classes optimisation causing the problem.  Note that
  enabling this option may result in more time being taken when
  populating a cold cache.
  

Problem summary

• In rare situations, a thread can take many seconds to attempt to
  load a class when the shared classes feature is enabled.
  
  This normally only occurs when multiple threads are attempting
  to load the same class simultaneously, and the class does not
  exist (java.lang.ClassNotFoundException would eventually be
  thrown).
  

Problem conclusion

• The JVM has been updated to resolve the performance problem.
  
  This defect will be fixed in:
  5.0.0 SR11 FP1
  

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

  JAVA 5 J9 COMMO

• Fixed component ID

  620500127

Applicable component levels

• R500 PSN

     UP