How to Monitor Java Memory Usage

How to monitor Java memory usage?

If you want to really look at what is going on in the VM memory you should use a good tool like VisualVM. This is Free Software and it's a great way to see what is going on.

Nothing is really "wrong" with explicit gc() calls. However, remember that when you call gc() you are "suggesting" that the garbage collector run. There is no guarantee that it will run at the exact time you run that command.

how to monitor the memory usage of a java program?

from JDK 6 onwards you have a tool in the bin directory which monitors CPU, memory consumption as well as the number of threads spawned. its called visualvm. Just start it and then start your java process. You will see the java process in the tool on the left hand side. Double click on the process and view the statistics. Hope this helps. :)

How to monitor Java Heap usage in Azure Monitor

Azure recommended way is to use Azure Monitor Application Insights Java 3.0 which does not require any code change to your application. You can take a look at detailed configuration ( especially the JMX counter) here which contains the heap memory.

<PerformanceCounters>
      <Jmx>
        <Add objectName="java.lang:type=ClassLoading" attribute="TotalLoadedClassCount" displayName="Loaded Class Count"/>
        <Add objectName="java.lang:type=Memory" attribute="HeapMemoryUsage.used" displayName="Heap Memory Usage-used" type="composite"/>
      </Jmx>
    </PerformanceCounters>

For adding alerts on these metrics you can consult the documentation here.

How to dynamically monitor Java heap size?

maxMemory() returns the maximum amount of memory that java will use. So That will not get you what you want. totalMemory() is what you are looking for though. See The docs

Monitoring Java internal objects & memory usage

To monitor the memory usage of a Java process, I'd use a JMX client such as JVisualVM, which is bundled with the Oracle JDK:

https://visualvm.java.net/jmx_connections.html

To identify the cause of a memory leak, I'd instruct the JVM to take a heap dump when it runs out of memory (on the Oracle JVM, this can be accomplished by specifying -XX:-HeapDumpOnOutOfMemoryError when starting your Java program), and then analyze that heap dump using a tool such as Eclipse MAT.

Monitor Java heap usage

• init

  represents the initial amount of memory (in bytes) that the Java virtual machine requests from the operating system for memory management during startup. The Java virtual machine may request additional memory from the operating system and may also release memory to the system over time. The value of init may be undefined.

• used

  represents the amount of memory currently used (in bytes).

• committed

  represents the amount of memory (in bytes) that is guaranteed to be available for use by the Java virtual machine. The amount of committed memory may change over time (increase or decrease). The Java virtual machine may release memory to the system and committed could be less than init. committed will always be greater than or equal to used.
  max represents the maximum amount of memory (in bytes) that can be used for memory management. Its value may be undefined. The maximum amount of memory may change over time if defined. The amount of used and committed memory will always be less than or equal to max if max is defined. A memory allocation may fail if it attempts to increase the used memory such that used > committed even if used <= max would still be true (for example, when the system is low on virtual memory).
  Below is a picture showing an example of a memory pool:

  +----------------------------------------------+
  +////////////////           |                  +
  +////////////////           |                  +
  +----------------------------------------------+
  
  |--------|
     init
  |---------------|
         used
  |---------------------------|
            committed
  |----------------------------------------------|
  

• Non-Heap memory (~Perm)

  Also, the JVM has memory other than the heap, referred to as non-heap memory. It is created at the JVM startup and stores per-class structures such as runtime constant pool, field and method data, and the code for methods and constructors, as well as interned Strings.

how to monitor java heap memory usage in jboss eap production server

You can use Jboss CLI to check JVM memory details,

• Connect to the JBoss using CLI:

./jboss-cli.sh -c --controller=localhost:9999

• Getting the JVM Memory details:

/core-service=platform-mbean/type=memory/:read-resource(recursive=true,proxies=true,include-runtime=true,include-defaults=true)

Or you can use JBoss management console,

• Go to Runtime tab
• Select JVM from Sytem status

Or you can use JConsole

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