2009 JavaOne: VisualVM

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How To Get VisualVM

The best part of VisualVM is that it's in your JDK bin directory already, if you've got any version of JDK1.6 since update 7. To run it, just click on the jvisualvm.exe icon.
All you need to do is click on the jvisualvm.exe and the application starts up. All Java applications running will be displayed on the right hand side navigation bar. Note that there is no need to register your application with VisualVM - it'll appear automatically. You can also view remote applications in this navigator.

That unknown application (pid 5392) is Eclipse.

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Using VisualVM

The list of features available is pretty impressive. VisualVM allows you to:

    * Monitor application performance and memory consumption
    * Monitor application threads
    * Profile application performance and analyze memory allocation
    * Take thread or heap dumps
    * Analyze core dumps
    * Save snapshots to analyze the application offline.

You'll find instructions on how all of these features work in our previous post on the topic, as well as in the VisualVM getting started documentation.

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An IDE Comparison with VisualVM

I wanted to do something different in my use of VisualVM, so I decided that I would do a comparison of the three leading IDEs. I did a fresh install of NetBeans 6.5.1 (JavaSE only version), Eclipse (for Java Developers) and IntelliJ IDEA (8.1.2).

The test is as follows:

    * Run the Memory Profiler in VisualVM
    * Create a new project in the IDE
    * Create a simple class with a main method printing Hello World
    * Save the Memory Profiler results
    * Get a Heap Dump of the application
    * Get information from the Monitor view in VisualVM
    * Restart the IDE and using the CPU Profiler, perform the same steps in the IDE
    * Save CPU Profiler results

I realise that both the CPU and Memory Profiling could have been done simultaneously, but for the purpose of this article I wanted to keep them seperate.

When I ran the IntelliJ tests I had to start it up with my own JDK rather than the IntelliJ one. I'm unfamiliar with the IDE, but I noticed it had to parse the files in the JDK when I created a new project with the JSDK.

Also, it's fair to note that I've just downloaded the default distributions of these IDEs, without trimming them down to the minimum for Java development.

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Heap Dump

I found the best means for comparison across the applications was the Heap Dump. This is really easy to do - at any stage during the application run, right click on the application in VisualVM and select Heap Dump.

The criteria I will compare here is the total bytes and total classes.

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NetBeans Heap Dump

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Eclipse Heap Dump

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IntelliJ :

    * Total Bytes:   76,582,715   
    * Total Classes: 14,368

Eclipse:

    * Total Bytes:   62,112,960
    * Total Classes: 11,428


NetBeans:

    * Total Bytes:   31,576,772
    * Total Classes: 10,583

It's clear here the NetBeans is the one that'll use up less of the heap using half the bytes that Eclipse needs. IntelliJ seems to need a lot more.

The Monitor View is also interesting to look at as your application is running. Here I simply looked at the threaded local classes. Eclipse almost hits 25K, IntelliJ gets closer to 27K, while NetBeans stays below 20K

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Memory & CPU Profile Results

I noticed that when I started profiling, that I needed to wait for instrumentation to be performed on the classes and methods. For the IDEs this took a significant, but not unreasonable, amount of time.
Memory and CPU profiling isn't that useful for a comparison of products. Where profiling comes in handy is when you need to find where leaks exist in your application. Nevertheless, here are the results of the profiling for the IDEs.

It's interesting to look at the common objects between the IDEs. For example, byte[] is heavily utilized in NetBeans, but to a lesser extent in both Eclipse and IntelliJ. We do see a significant use of char[] on all IDE's

    * NetBeans : 19.6% of memory
    * Eclipse  : 31.6% of memory
    * IntelliJ : 32.7% of memory

NetBeans Memory Profiler View

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NetBeans Memory Profiler View

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Eclipse Memory Profiler View