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I'm using jstat to collect jvm metrics and push them to graphite through collectd. A few days ago i noticed that i had "spikes" in the graphs regarding Old Space, but those were not triggering any full GCs, which lead me to thinking that the metric was off. So i started looking at jstat's output, searching for such a metric to pop and here it is :

jstat -gccause 123456 1s

S0     S1     E      O      M     CCS    YGC     YGCT    FGC    FGCT     GCT    LGCC                 GCC
27,81   0,00  49,52  63,18  65,05  48,04   7146  703,497    20   10,564  714,061 Allocation Failure   No GC
27,81   0,00  63,65  63,18  65,05  48,04   7146  703,497    20   10,564  714,061 Allocation Failure   No GC
27,81  16,89 100,00  99,93  65,05  48,04   7147  703,497    20   10,564  714,061 Allocation Failure   Allocation Failure
0,00  23,40  10,34  63,19  65,05  48,04   7147  703,621    20   10,564  714,185 Allocation Failure   No GC
0,00  23,40  35,39  63,19  65,05  48,04   7147  703,621    20   10,564  714,185 Allocation Failure   No GC

As you can see, my Old space is increasing normally and just "peaks" to 99.93%, not triggering any full GC and returns to a normal metric right after that.

So i'm wondering if something's off or if it's just an incorrect iteration.

Thanks !

user1159791
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  • It also shows both survivor spaces in use at the same time which you shouldn't be able to see. I would look at the other gc capacity information and you might see whether the usage or the maximum is information or both. – Peter Lawrey Mar 06 '15 at 13:28
  • Thanks for your answer. I'm sorry i didn't get what i should be looking for with another gc option ? what do you mean by "whether the usage or the maximum is information or both" ? – user1159791 Mar 06 '15 at 13:31
  • `jstat -options` lists the gc options `-gc -gccapacity -gccause -gcmetacapacity -gcnew -gcnewcapacity -gcold -gcoldcapacity -gcutil` I suggest trying `-gccapacity` to see more detail. – Peter Lawrey Mar 06 '15 at 13:35
  • I don't think it will fix your problem but might give a better idea why this is happening. If it is a bug in the JVM, I suggest making sure you have the latest update for your version of Java. e.g. Java 6 update 67 or Java 7 update 45 or Java 8 update 40. – Peter Lawrey Mar 06 '15 at 13:38

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