Long garbage collection pause due to single-threaded CMS initial mark

Solution Unverified - Updated

Environment

  • OpenJDK
  • Oracle JDK
  • CMS (low pause) collector

Issue

  • CMS initial mark phase is serial / single-threaded (user ~= real time):
[GC [1 CMS-initial-mark: 1962869K(8388608K)] 2380861K(10424128K), 4.7281533 secs] [Times: user=4.74 sys=0.01, real=4.73 secs]

Resolution

Add -XX:+CMSParallelInitialMarkEnabled (JDK7), or replace -XX:-CMSParallelInitialMarkEnabled with -XX:+CMSParallelInitialMarkEnabled to enable multi-threaded initial marking.

Root Cause

CMS initial marking is disabled by default in JDK7. It can also be disable with the -XX:-CMSParallelInitialMarkEnabled (note - vs +).

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