Java GC Tutorials - Herong's Tutorial Examples

∟Outdated Tutorials

∟Outdated: 441/400/40MB Test on JRockit 28.2

This section provides a tutorial example on running GCTest2.java on JRockit 28.2.7 with 441MB memory limit and a 400MB base plus 40MB fluctuating memory usage with object size of 1.25MB. 1 extra MB is enough for the GC to work.

From the previous tutorial, we learned that JRockit GC behaves better than HotSpot with low free memory. In this tutorial, I want to how low it can go with HotSpot R28.2.7 on my Windows 7 system: 

>\Progra~1\java\jrockit-jdk1.6.0_45-R28.2.7-4.1.0\bin\javac 
   GCTest2.java

>\Progra~1\java\jrockit-jdk1.6.0_45-R28.2.7-4.1.0\bin\java 
   -Xmx441m 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  451584   790  450794  0%  450560  409600  40960  234
  3  451584   790  450794  0%  450560  409600  40960  234
  4  451584   790  450794  0%  450560  409600  40960  234
  5  451584   792  450792  0%  450560  409600  40960  232
  6  451584   792  450792  0%  450560  409600  40960  232
  7  451584   792  450792  0%  450560  409600  40960  232
  8  451584   792  450792  0%  450560  409600  40960  232
 10  451584   792  450792  0%  450560  409600  40960  232
 11  451584   792  450792  0%  450560  409600  40960  232
 12  451584   790  450794  0%  450560  409600  40960  234
 13  451584   790  450794  0%  450560  409600  40960  234
 14  451584   791  450793  0%  450560  409600  40960  233
 15  451584   790  450794  0%  450560  409600  40960  234
 17  451584   790  450794  0%  450560  409600  40960  234
 18  451584   792  450792  0%  450560  409600  40960  232
 19  451584   792  450792  0%  450560  409600  40960  232
 20  451584   790  450794  0%  450560  409600  40960  234
 21  451584   790  450794  0%  450560  409600  40960  234
 23  451584   790  450794  0%  450560  409600  40960  234
 24  451584   792  450792  0%  450560  409600  40960  232
 25  451584   790  450794  0%  450560  409600  40960  234
 26  451584   790  450794  0%  450560  409600  40960  234
 27  451584   791  450793  0%  450560  409600  40960  233
 29  451584   790  450794  0%  450560  409600  40960  234
 30  451584   790  450794  0%  450560  409600  40960  234
 31  451584   792  450792  0%  450560  409600  40960  232
 32  451584   792  450792  0%  450560  409600  40960  232
 33  451584   790  450794  0%  450560  409600  40960  234
 35  451584   790  450794  0%  450560  409600  40960  234
 36  451584   792  450792  0%  450560  409600  40960  232
 37  451584   792  450792  0%  450560  409600  40960  232
 38  451584   790  450794  0%  450560  409600  40960  234
 39  451584   790  450794  0%  450560  409600  40960  234
 41  451584   792  450792  0%  450560  409600  40960  232
 42  451584   790  450794  0%  450560  409600  40960  234
 43  451584   790  450794  0%  450560  409600  40960  234
 44  451584   792  450792  0%  450560  409600  40960  232
 45  451584   792  450792  0%  450560  409600  40960  232
 47  451584   790  450794  0%  450560  409600  40960  234
 48  451584   790  450794  0%  450560  409600  40960  234
 49  451584   790  450794  0%  450560  409600  40960  234
 50  451584   792  450792  0%  450560  409600  40960  232
 51  451584   792  450792  0%  450560  409600  40960  232
...                                                       
380  451584   790  450794  0%  450560  409600  40960  234
381  451584   792  450792  0%  450560  409600  40960  232
382  451584   790  450794  0%  450560  409600  40960  234
384  451584   792  450792  0%  450560  409600  40960  232
...

The result is very impressive. JRockit JVM R28.2.7 requires only 441MB to run a program that has a 400MB base memory usage plus 40MB fluctuating memory usage with object size of 1.25MB. Basically, the JRockit GC requires only 1MB to manage dead objects and other system tasks.

But please note that JRockit must run GC much more frequently than HotSpot to support this low free memory situation. This will definitely impact the execution time performance of the application.

Last update: 2014.

Table of Contents

 About This Book

 Heap Memory Area and Size Control

 JVM Garbage Collection Logging

 Introduction of Garbage Collectors

 Serial Collector - "+XX:+UseSerialGC"

 Parallel Collector - "+XX:+UseParallelGC"

 Concurrent Mark-Sweep (CMS) Collector - "+XX:+UseConcMarkSweepGC"

 Garbage First (G1) Collector - "+XX:+UseG1GC"

 Object References and Garbage Collection

 Garbage Collection Performance Test Program

 Performance Tests on Serial Collector

 Performance Tests on Parallel collector

 Performance Tests on Concurrent collector

 Performance Tests on G1 collector

 Garbage Collection Performance Test Summary

►Outdated Tutorials

 Outdated: GCTest2.java - Garbage Collection Test Program

 Outdated: 640/400/40MB Test on HotSpot Client 1.7

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

 Outdated: 640/400/40MB Test on JRockit 28.2

►Outdated: 441/400/40MB Test on JRockit 28.2

 Outdated: 1076/800/80MB Test on HotSpot Client 1.7

 Outdated: 1076/800/80MB Test on HotSpot Client 1.6

 Outdated: 1076/800/80MB Test on JRockit 28.2

 References

 Full Version in PDF/EPUB