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Tag Archives: JVM

Busting PermGen Myths

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In my latest post I explained the reasons that can cause the java.lang.OutOfMemoryError: PermGen space crashes. Now it is time to talk about possible solutions to the problem. Or, more precisely, about what the Internet suggests for possible solutions. Unfortunately, I can only say that I felt my inner Jamie Hyneman from MythBusters awakening when going through the different “expert ...

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What is a PermGen leak?

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What follows is a practical introduction to a specific type of memory problems in Java applications. Namely – we will analyze the errors that cause the java.lang.OutOfMemoryError: PermGen space symptom in the stack trace. First of all we will go through the core concepts required to understand the subject – and explain what objects, classes, classloaders and the JVM memory ...

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How much memory do I need

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What is retained heap? How much memory will I need? This is a question you might have asked yourself (or others) when building a solution, creating a data structure or choosing an algorithm. Will this graph of mine fit in my 3G heap if it contains 1,000,000 edges and I use a HashMap to store it? Can I use the ...

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When using direct memory can be faster

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Overview Using direct memory is no guarantee of improving performance.  Given it adds complexity, it should be avoided unless you have a compelling reason to use it. This excellent article by Sergio Oliveira Jr shows its not simply a matter of using direct memory to improve performance Which one is faster: Java heap or native memory? Where direct memory and memory mapped files ...

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Java Heap Dump: Are you up to the task?

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If you are as much enthusiasm as I am on Java performance, heap dump analysis should not be a mystery to you. If it is then the good news is that you have an opportunity to increase your Java troubleshooting skills and JVM knowledge. The JVM has now evolve to a point that it is much easier today to generate ...

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IBM AIX: Java process size monitoring

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This article will provide you with a quick reference guide on how to calculate the Java process size memory footprint for Java VM processes running on IBM AIX 5.3+ OS. This is a complementary post to my original article on this subject: how to monitor the Java native memory on AIX. I highly recommend this read to any individual involved ...

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Compact Off-Heap Structures/Tuples In Java

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In my last post I detailed the implications of the access patterns your code takes to main memory. Since then I’ve had a lot of questions about what can be done in Java to enable more predictable memory layout. There are patterns that can be applied using array backed structures which I will discuss in another post. This post will ...

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JavaOne 2012: Diagnosing Your Application on the JVM

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It was worth attending Staffan Larsen‘s (Oracle Java Serviceability Architect) presentation ‘Diagnosing Your Application on the JVM‘ (Hilton Plaza A/B) just for learning of the new jcmd command-line tool provided with Oracle’s JVM 7. The rest of the presentation was ‘bonus’ for me, which was nice for the last session I attended on Wednesday of JavaOne 2012. The Oracle HotSpot ...

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