how to take jave heap dump every 30 seconds using kill -3 <pid> command

Question

Please help in this, i want to run a shell script where it should take jave heap dump every 30 seconds using kill -3 command. Thanks in advance.

Answer 1

Have you tried such a simple shell script?

while true
do
  jmap -dump:file=/tmp/java-`date +%s`.hprof PID_OF_JVM
  sleep 30
done

This will create one file pear each snapshot. For thread dump you can use similar script:

while true
do
  jstack PID_OF_JVM > stack-`date +%s`.txt
  sleep 30
done

I guess you can use kill -3 instead of jstack .

Answer 2

you can do thread dumping from java application using code like this

 public static String getDumpFor(Thread thread) {
    StringBuilder sb = new StringBuilder();
    if (thread.isAlive()) {
        StackTraceElement[] stackTrace = thread.getStackTrace();
        sb.append(thread.toString()).append("\n")
                .append(String.format(" State - %s,", thread.getState()))
                .append(String.format(" Is daemon = %s,", thread.isDaemon()));
        for (StackTraceElement s : stackTrace)
            sb.append("\tat ").append(s.getClassName()).append(".").append(s.getMethodName()).append("(").append(s.getFileName()).append(":").append(s.getLineNumber()).append(")")
                    .append("\n");
    }
    return sb.toString();
}


public static void dumpActiveThreads() {
    Map<Thread, StackTraceElement[]> stackTraces = Thread.getAllStackTraces();
    Set<Thread> keySet = stackTraces.keySet();
    System.out.println("\nThread dump begin:");
    for (Thread thread : keySet)
        dumpActiveThread(thread);
    System.out.println("\nThread dump end.");

}

and then schedule task like this

 final ScheduledFuture<?> scheduledFuture = scheduledExecutorService.scheduleWithFixedDelay(
            new Runnable() {dumpActiveThreads()},
            0,
            30, TimeUnit.SECONDS);

Answer 3

I have not used kill -3 command but i have used jmap command provided by sun sdk

You can write a script and then in script run below command.

${JAVA_HOME}/bin/jmap -dump:file=/home/MyDump.hprof PID

Answer 4

3 will give only the thread dump but not the heap dump.Thread dump means you can only check the stack traces for each thread in the JVM.But you are lookin g for the heap dump on linux then need to use the below commands. jmap -dump:file=myheap.bin {pid of which you are looking to take heap dump}. The output "myheap.bin" is not human readable,to read the file you can use the MAT tool. MAT download link: http://www.eclipse.org/mat/