IV50585: GC STORM WHEN JAVA.IO.BITS.RESERVEMEMORY IN MULTI THREAD ENV

APAR status

• Closed as program error.

Error description

• Error Message: In workloads with high numbers of paralell
  threads that use DriectByteBuffers, like in almost any WAS
  deployment, where a volume of direct memory is required that is
  larger than the default soft limit (but unknown outside runtime
  demands) it will end up in a situation whee multiple threads are
  all hitting the soft limits at the same time. It will cause GC
  storm
  .
  Stack Trace: N/A
  .
  N/A
  

Local fix

• N/A
  

Problem summary

• When multiple threads enter Bits.reserveMemoty() at same time,
  threads pass the initial synchronized block quickly but gc
  triggered by first thread has not yet finished, so all threads
  will fail to reserve memory and trigger gc in its own thread.
  This causes gc storm.
  

Problem conclusion

• This defect will be fixed in:
  7.0.0 SR6
  .
  The solution is move check and increase Max memory codes to the
  end of initial synchronized block, so that only the first thread
  will trigger gc and the following threads will reserve memory
  successfully in initial synchronized block.
  

Temporary fix

• N/A
  

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 CLASS LIBS

• Fixed component ID

  620700130

Applicable component levels

• R700 PSY

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