Beaware!!! with NewRatio while using Concurrent Mark Sweep GC as Garbage Collector

In Sun JDK there were few bugs previously with subject “JDK-6872335 : NewRatio ignored when UseConcMarkSweepGC set”.

http://bugs.java.com/view_bug.do?bug_id=6872335

http://bugs.java.com/view_bug.do?bug_id=6862534

Although these bugs are fixed, but IMO the bug still exists for default settings of NewRatio when UseConcMarkSweepGC is used.

We still have the bug where the default NewRatio=2 is not considered along with UseConcMarkSweepGC

Option #1 : Default GC (-XX:+UseParallelGC) : PSYoungGen      total 1835008K = 1.75GB (As it considered the default NewRatio=2)

# /usr/bin/java -server -Xms6144m -Xmx6144m -XX:MaxMetaspaceSize=256m -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -version

-XX:InitialHeapSize=6442450944 -XX:MaxHeapSize=6442450944 -XX:MaxMetaspaceSize=268435456 -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseParallelGC

java version "1.8.0_60"

Java(TM) SE Runtime Environment (build 1.8.0_60-b27)

Java HotSpot(TM) 64-Bit Server VM (build 25.60-b23, mixed mode)

Heap

PSYoungGen      total 1835008K, used 94372K [0x0000000740000000, 0x00000007c0000000, 0x00000007c0000000)

  eden space 1572864K, 6% used [0x0000000740000000,0x0000000745c29180,0x00000007a0000000)

  from space 262144K, 0% used [0x00000007b0000000,0x00000007b0000000,0x00000007c0000000)

  to   space 262144K, 0% used [0x00000007a0000000,0x00000007a0000000,0x00000007b0000000)

ParOldGen       total 4194304K, used 0K [0x0000000640000000, 0x0000000740000000, 0x0000000740000000)

  object space 4194304K, 0% used [0x0000000640000000,0x0000000640000000,0x0000000740000000)

Metaspace       used 2189K, capacity 4480K, committed 4480K, reserved 1056768K

  class space    used 240K, capacity 384K, committed 384K, reserved 1048576K

[root@vl-aus-sln-pt39 ~]#

Option #2 : UseConcMarkSweepGC only (-XX:+ UseConcMarkSweepGC) : par new generation   total 153344K = 149.75 MB (Here –XX:NewRatio=2 is ignored which is set by default)

# /usr/bin/java -server -Xms6144m -Xmx6144m -XX:MaxMetaspaceSize=256m -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -XX:+UseConcMarkSweepGC -version

-XX:InitialHeapSize=6442450944 -XX:MaxHeapSize=6442450944 -XX:MaxMetaspaceSize=268435456 -XX:MaxNewSize=174485504 -XX:MaxTenuringThreshold=6 -XX:NewSize=174485504 -XX:OldPLABSize=16 -XX:OldSize=348971008 -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseConcMarkSweepGC -XX:+UseParNewGC

java version "1.8.0_60"

Java(TM) SE Runtime Environment (build 1.8.0_60-b27)

Java HotSpot(TM) 64-Bit Server VM (build 25.60-b23, mixed mode)

Heap

par new generation   total 153344K, used 8179K [0x0000000640000000, 0x000000064a660000, 0x000000064a660000)

  eden space 136320K,   6% used [0x0000000640000000, 0x00000006407fcf00, 0x0000000648520000)

  from space 17024K,   0% used [0x0000000648520000, 0x0000000648520000, 0x00000006495c0000)

  to   space 17024K,   0% used [0x00000006495c0000, 0x00000006495c0000, 0x000000064a660000)

concurrent mark-sweep generation total 6121088K, used 0K [0x000000064a660000, 0x00000007c0000000, 0x00000007c0000000)

Metaspace       used 2190K, capacity 4480K, committed 4480K, reserved 1056768K

  class space    used 240K, capacity 384K, committed 384K, reserved 1048576K

[root@vl-aus-sln-pt39 ~]#

Option #3 : UseConcMarkSweepGC along with NewRatio=2 (-XX:+ UseConcMarkSweepGC –XX:NewRatio=2) : par new generation   total 1887488K = 1.8 GB (Here –XX:NewRatio=2 is considered when set explicitly)

# /usr/bin/java -server -Xms6144m -Xmx6144m -XX:MaxMetaspaceSize=256m -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -XX:+UseConcMarkSweepGC -XX:NewRatio=2 -version

-XX:InitialHeapSize=6442450944 -XX:MaxHeapSize=6442450944 -XX:MaxMetaspaceSize=268435456 -XX:MaxTenuringThreshold=6 -XX:NewRatio=2 -XX:OldPLABSize=16 -XX:+PrintCommandLineFlags -XX:+PrintGCDetails -XX:+UseCompressedClassPointers -XX:+UseCompressedOops -XX:+UseConcMarkSweepGC -XX:+UseParNewGC

java version "1.8.0_60"

Java(TM) SE Runtime Environment (build 1.8.0_60-b27)

Java HotSpot(TM) 64-Bit Server VM (build 25.60-b23, mixed mode)

Heap

par new generation   total 1887488K, used 100669K [0x0000000640000000, 0x00000006c0000000, 0x00000006c0000000)

  eden space 1677824K,   6% used [0x0000000640000000, 0x000000064624f7f0, 0x00000006a6680000)

  from space 209664K,   0% used [0x00000006a6680000, 0x00000006a6680000, 0x00000006b3340000)

  to   space 209664K,   0% used [0x00000006b3340000, 0x00000006b3340000, 0x00000006c0000000)

concurrent mark-sweep generation total 4194304K, used 0K [0x00000006c0000000, 0x00000007c0000000, 0x00000007c0000000)

Metaspace       used 2189K, capacity 4480K, committed 4480K, reserved 1056768K

  class space    used 240K, capacity 384K, committed 384K, reserved 1048576K

[root@vl-aus-sln-pt39 ~]#

Set the New Ratio explicitly if we are using ConcMarkSweepGC  .