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Editorial Team
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Asked: 2026-06-02T13:52:42+00:00

I’m wondering what are the exact situations that trigger Full Garbage Collection in Java.

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I’m wondering what are the exact situations that trigger Full Garbage Collection in Java.

The obvious ones are:

  • Running out of old gen
  • Running out of perm gen
  • Calling System.gc()

What about other cases that cause full gc? Particularly:

  • Not having enough free space in Survivor Space to copy objects from Eden.
  • Minor collections not being able to cope with allocation rate of new objects (don’t know how though).

I’m running Sun Java 1.6 and using Concurrent Mark-Sweep and ParNew for new gen.

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1 Answer

  1. Editorial Team

    I’ve observed one more situation that triggers a full GC in Java Hotspot VM 1.6 64bit on Ubuntu, using Concurrent Mark-Sweep:

    If -XX:PermSize value does not equal to -XX:MaxPermSize (e.g. is smaller), an occasional Full GC happens when java needs to expand the PermGen (even though it does not need to allocate more memory than MaxPermSize).
    So setting -XX:PermSize and -XX:MaxPermSize to be the same seems like a good idea.

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