Outdated: 640/400/40MB Test on HotSpot Client 1.6

Java 8 GC Tutorials - Herong's Tutorial Examples

∟Outdated: 640/400/40MB Test on HotSpot Client 1.6

This section provides a tutorial example on running GCTest2.java on HotSpot Client JVM 1.6.0_45 with 640MB memory limit and a 400MB base plus 40MB fluctuating memory usage with object size of 1.25MB.

As a comparison, I ran GCTest2.java with the same parameters on HotSpot Client 1.6.0_45 my Windows 7 system:

>\Progra~1\java\jdk1.6.0_45\bin\javac GCTest2.java

>\Progra~1\java\jdk1.6.0_45\bin\java -Xmx640m GCTest2
Test parameters:
   Object size: 1280KB
   Initial objects and data size: 320, 409600KB
   Added objects and data size: 32, 40960KB
Time   Total    Free    Used  Free  Total    Act.    Dead    Over
sec.    Mem.    Mem.    Mem.    %.   Obj.    Obj.    Obj.    Head
   1  633536  182807  450729  28%  450560  409600   40960     169
   2  633536  141849  491687  22%  450560  409600   40960   41127
   3  633536  100888  532648  15%  491520  409600   81920   41128
   4  633536   59928  573608   9%  532480  409600  122880   41128
   5  633536   18967  614569   2%  573440  409600  163840   41129
   7  633536    7448  626088   1%  450560  409600   40960  175528
   8  633536  141860  491676  22%  450560  409600   40960   41116
   9  633536  100900  532636  15%  491520  409600   81920   41116
  10  633536   59939  573597   9%  532480  409600  122880   41117
  11  633536   18971  614565   2%  573440  409600  163840   41125
  12  633536   18976  614560   2%  450560  409600   40960  164000
  13  633536  141864  491672  22%  450560  409600   40960   41112
  14  633536  100900  532636  15%  491520  409600   81920   41116
  15  633536   59940  573596   9%  532480  409600  122880   41116
  16  633536   18976  614560   2%  573440  409600  163840   41120
  18  633536   18979  614557   2%  450560  409600   40960  163997
  19  633536  141866  491670  22%  450560  409600   40960   41110
  20  633536  100903  532633  15%  491520  409600   81920   41113
  21  633536   59939  573597   9%  532480  409600  122880   41117
  22  633536   18976  614560   2%  573440  409600  163840   41120
  23  633536  182827  450709  28%  450560  409600   40960     149
  24  633536  141865  491671  22%  491520  409600   81920     151
  25  633536  100902  532634  15%  532480  409600  122880     154
  26  633536   59938  573598   9%  573440  409600  163840     158
  27  633536   18975  614561   2%  614400  409600  204800     161
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
        at GCTest2$MyObject.<init>(GCTest2.java:70)
        at GCTest2.myTest(GCTest2.java:37)
        at GCTest2.main(GCTest2.java:22)

Conclusion, HotSpot Client JVM 1.6.0_45 requires more than 640MB to run a program that has a 400MB base memory usage plus 40MB fluctuating memory usage with object size of 1.25MB. Basically, the JVM requires more than 200MB to manage dead objects and other system tasks.