GC related diag messages accumulating in Java heap

Thomas Viessmann thomas.viessmann at oracle.com
Wed Jul 3 08:07:47 UTC 2013


Hi all,


in a Java heap dump of 7u21 we can see accumulating tons of GC related 
diagnostics message strings.
This will result in an OOME finally. These millions of strings are e.g.:

"end of minor GC", "end of major GC",  "Copy",  "Allocation Failure", 
"PS Scavenge"

Interestingly these stings are root objects and are never been 
collected. What is
the purpose of these messages? Are they supposed to go into a logfile?
We didn't see them anywhere.

And what JVM flag needs to be enabled to trigger their creation?

 From memoryManager.cpp

     if (*is_notification_enabled()*) {
     320       bool isMajorGC = this == 
MemoryService::get_major_gc_manager();
     321       GCNotifier::pushNotification(this, isMajorGC ? "end of 
major GC" : "end of minor GC",
     322 GCCause::to_string(cause));


In other words, how can we set the boolean _notification_enabled to 
false in order to suppress
the creation of these annoying strings?

Further on I'm wondering why these strings are being created in Java 
heap rather than as internal strings
in perm in order to avoid millions of duplicates.

Right now I consider this a bug which is btw not reproducible with 
JRockit and also not reproducible
with Java SE 6. Only 7.


Thanks and Regards

Thomas




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