Free Java Profiling Tools

by Calvin Austin Finding a memory leak in a Java application can be one of the more difficult tasks a Java developer has to handle. The Java virtual machine effectively manages most of the memory an application uses so a 'memory leak' is really down to a reference that can't be recovered due to a variety of reasons. These leaks are often small and take a while to show up in your application.

To simply see what the JVM is doing with its memory management and see a leak in progress you can use one of the following options to the JVM 

java ­-XX:+ PrintGCDetails 
java ­-verbose:gc 
jmap ­-heap or ­jmap -histo (JDK 5.0)

For example: 

[#]$ jmap ­-histo 362 
Attaching to process ID 362, please wait... 
... 
Object Histogram: 
Size Count Class description ­
149232 167 char[] 
34160 14 byte[] 
8352 29 * ObjArrayKlassKlass 
7600 203 java.lang.Object[] 
3792 158 java.lang.String 
3696 42 java.lang.Class 
2360 23 * ConstMethodKlass

and also 

jmap ­-heap 
Heap Configuration: 
MinHeapFreeRatio = 40 
MaxHeapFreeRatio = 70 
MaxHeapSize = 67108864 (64.0MB) 
NewSize = 655360 (0.625MB) 
MaxNewSize = 4294901760 (4095.9375MB) 
OldSize = 1441792 (1.375MB) 
NewRatio = 12 SurvivorRatio = 8 
PermSize = 8388608 (8.0MB) MaxPermSize = 67108864 (64.0MB)

For a graphical representation of memory use there are 3 tools. HAT, jconsole and visualgc

HAT or heap analyis tools is available from java.net

First create a profiling output, this file is generated when the application ends or ctrl-c is pressed. 

java -agentlib:hprof=heap=all,format=b

This then creates a java.hprof file. Supply this file as an option to hat 

hat java.hprof

Then point your browser to localhost:7000. hat starts a mini http server for you to browser the profiling output

jconsole is available in the JDK 5.0 bin directory. You start your application with jmx management enabled 

java -Dcom.sun.management.jmxremote

Then simply launch jconsole, it will ask you which jvm to attach to.


visualgc comes in a package called jvmstat from java.net to run it you need to execute bin/visualgc and supply the process (or jvm identifier) and and interval or use the default of 500ms


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This page was last modified 01:56, 1 April 2006.