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Tag Archives: JVM

Java Flight Recorder (JFR)

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JFR is a Java profiler which will allow you to investigate the runtime characteristics of your code. Typically you will use a profiler to determine which parts of your code are causing  large amounts of memory allocation or causing excess CPU to be consumed. There are plenty of products out there.  In the past I’ve used YourKit, OptimizeIt, JProfiler, NetBeans ...

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JVM is down with “OutOfMemory” error – what should I do?

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Amazing as it may seem, but this particular cry “From the Depths” is frequently displayed among the results of search requests regarding JVM settings. You have probably been faced with the “I remember that option, but how to enable it” problem, while administrating servers or adjusting virtual appliances at times (semi-annualy, for example) and apart from your main tasks. There ...

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Starting multiple JBoss A-MQ JVMs on the same machine

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So I haven’t been blogging as much recently — just been really busy. But my New Year’s resolution is to blog a little more sharing some things I come across frequently, even if it’s simple stuff that might help some people out. So for this entry, I’ll show a quick way to start up multiple JBoss A-MQ instances on a ...

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Testing JVM server-side JavaScript with Jasmine, Spock and Nashorn

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JavaScript usage is not limited to client-side code in browser or NodeJS powered server-side code. Many JVM based projects are using it as internal scripting language. Testing this sort of functionality is neither straightforward nor standard. In this post I intend to demonstrate an approach for testing JavaScript in server-side JVM environment using mature tools like Jasmine, Spock and Nashorn. ...

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cjmx: A command-line version of JConsole

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JConsole is a nice tool when it comes to monitoring a running Java application. But when it is not possible to connect to a JVM with JConsole directly (due to network restrictions for example) and SSH tunneling is not possible, then it would be great to have a command line version of JConsole. jcmx is such a command line version ...

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On heap vs off heap memory usage

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Overview I was recently asked about the benefits and wisdom of using off heap memory in Java. The answers may be of interest to others facing the same choices. Off heap memory is nothing special. The thread stacks, application code, NIO buffers are all off heap.  In fact in C and C++, you only have unmanaged memory as it does not have ...

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Self-healing JVM

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This post is an example about an application where the first solution to each and every IT problem – “have you tried turning it off and on again” – can backfire and do more harm than good. Instead of turning things off and on, we have an application that can literally heal itself: it fails at the beginning, but starts ...

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Java performance tuning survey results (part IV)

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This is the last post in series where we analyze the results of the Java Performance Tuning Survey we conducted in October 2014. If you have not read the first posts, I recommend to go through the following first:                 Frequency and severity of performance problems Most popular monitoring solutions Tools and techniques ...

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