IV47984: LONG GC PAUSE TIMES WHEN USING WIDE CLASS HIERARCHIES

APAR status

• Closed as program error.

Error description

• Error Message: The problem presents as long pauses during which
  the application appears to hang. Taking a verbose GC log shows
  that each pause is associated with an unusually long GC event.
  The problem is associated with the use of very wide class
  inheritance trees, often due to the use of an application
  framework with an abstract base class which is sub-classed many
  thousands of times by the application.
  .
  Stack Trace: N/A
  .
  

Local fix

• The problem can be avoided by disabling the use of class
  hierarchy information during JIT compilation by using the
  following Java command line option:
  -Xjit:disableCHOpts,disableCHTable
  

Problem summary

• Very wide class hierarchies cause the JIT to collect excessive
  amounts of metadata about the resulting compiled code if certain
  optimisations are used. This metadata has to be cleaned up after
  class unloading which results in the long GC times.
  

Problem conclusion

• This defect will be fixed in:
  6.0.0 SR15
  7.0.0 SR6
  6.0.1 SR7
  5.0.0 SR16 FP4
  .
  The JIT has been modified to avoid collecting the metadata if a
  wide class hierarchy is detected for the method being compiled.
  

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:

  IV47990

Fix information

• Fixed component name

  JIT

• Fixed component ID

  620700124

Applicable component levels

• R600 PSY

     UP

• R260 PSY

     UP