IV26401: REDUCED PERFORMANCE AFTER HEAVY CLASS RE-LOADING

APAR status

• Closed as program error.

Error description

• After very extensive class-reloading, an application may
  demonstrate reduced performance.
  
  If run with -Xjit:verbose={compile*},vlog=jit.log, the log will
  contain "CACHES FULL" messages.
  

Local fix

• There is no completely effective work-around for this issue, but
  it is possible that using the following options to increase the
  size of each code cache and to allow for more memory to be used
  for code cache space will extend the time before performance is
  affected.
  
  Use 32MB code cache segments:
  -Xcodecache32m
  
  Allow up to 256MB of total code cache space:
  -Xjit:codetotal=262144
  
  Note that the -Xjit:codetotal option is not supported for use
  except at the direction of IBM Support in the course of Problem
  Resolution and Diagnosis.
  

Problem summary

• The problem occurs when an extreme amount of Java code needs to
  be compiled by the JIT in order to maintain application
  performance. Typically this can only happen when a frame-work is
  used which continually generates new classes, uses them briefly
  and then unloads them.
  

Problem conclusion

• This defect will be fixed in:
  5.0.0 SR15
  .
  An option has been added to the JIT to cause it to try harder to
  re-use memory from compiled classes which have been unloaded
  from the VM. Since this option is likely to be needed only in
  very special cases and may have a negative effect under more
  normal cases, it is not turned on by default. To enable the new
  behaviour the following option is required on the java command
  line:
  -Xjit:enableClearCodeCacheFullFlag
  

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 JIT

• Fixed component ID

  620500124

Applicable component levels

• R500 PSY

     UP