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Tag Archives: JVM

Add Some Entropy to Your JVM

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Being able to generate true random numbers depends on the entropy in your system. Some claim, that this can be guaranteed by fair dice roll. Others think that replacing the OpenJDK’s java.math.Random.nextInt() method with this body will help:                 public int nextInt() { return 14; } Source: http://www.redcode.nl/blog/2013/10/openjdk-and-xkcd-random-number/. But that’s absurd. We all know ...

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How To Write Your Own Java / Scala Debugger

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With this post we’ll explore how Java / Scala debuggers are written and work. Native debuggers such WinDbg for Windows or gdb for Linux/Unix get their power from hooks provided to them directly by the OS to monitor and manipulate the state of an external process. The JVM, acting as an abstraction layer on top of the OS, provides its ...

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Java Mission Control 5.2 is Finally Here! Welcome 7u40!

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It has been a while since we last heard of this fancy little thing called Mission Control. It came all the way from JRockit and was renamed to Java Mission Control. This is one of the parts which literally survived the convergence strategy between HotSpot and JRockit. With today’s Java SE 7 Update 40 you can actually use it again. ...

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Dealing With Slow Resource Leaks

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Finding resource leaks using Java-monitor Finding slow resource leaks is key to keeping your application servers up and running for very long times. Here I explain how I use Java-monitor to spot slow resource leaks and how to verify that they are actual leaks and not just extra pre-allocation into some HTTP connector or database pool. If you follow these ...

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Understanding the OutOfMemoryError

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Whenever you find yourself staring a stacktrace with OutOfMemoryError in it, it should all be crystal clear. The program has got no more elbow room and is dying just because of lack of it. From the 10,000 feet or executive chair this might already contain too much information. But those of you who have to build or maintain the applications ...

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5 Coding Hacks to Reduce GC Overhead

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In this post we’ll look at five ways in which we can use efficient coding to help our garbage collector spend less CPU time allocating and freeing memory, and reduce GC overhead. Long GCs can often lead to our code being stopped while memory is reclaimed (AKA “stop the world”). Some background The GC is built to handle large amounts ...

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Java Garbage Collection Distilled

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Serial, Parallel, Concurrent, CMS, G1, Young Gen, New Gen, Old Gen, Perm Gen, Eden, Tenured, Survivor Spaces, Safepoints, and the hundreds of JVM startup flags. Does this all baffle you when trying to tune the garbage collector while trying to get the required throughput and latency from your Java application? If it does then do not worry, you are not ...

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Java Just-In-Time compilation: more than just a buzzword

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A recent Java production performance problem forced me to revisit and truly appreciate the Java VM Just-In-Time (JIT) compiler. Most Java developers and support individuals have heard of this JVM run time performance optimization but how many truly understand and appreciate its benefits? This article will share with you a troubleshooting exercise I was involved with following the addition of ...

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Garbage Collection in Java (4)

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G1: Garbage First The G1 collector is the latest collector to be implemented in the hotspot JVM. Its been a supported collector ever since Java 7 Update 4. Its also been publicly stated by the Oracle GC Team that their hope for low pause GC is a fully realised G1. This post follows on from my previous garbage collection blog ...

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Micro jitter, busy waiting and binding CPUs

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Performance profiling a new machine When I work on a new machine, I like to get an understanding of it’s limitations.  In this post I am looking at the jitter on the machine and the impact of busy waiting for a new PC I built this weekend. The specs for the machine are interesting but not the purpose of the ...

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