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Tag Archives: JVM

QOTD: Java Thread vs. Java Heap Space

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The following question is quite common and is related to OutOfMemoryError: unable to create new native thread problems during the JVM thread creation process and the JVM thread capacity. This is also a typical interview question I ask to new technical candidates (senior role). I recommend that you attempt to provide your own response before looking at the answer.   ...

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Java heap space, native heap and memory problems

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Recently, I was discussing with a friend, why the Java process uses more memory than the maximum heap that we set when starting the java process. All java objects that code creates are created inside Java heap space, which its size is defined by the -Xmx option. But a java process is consisted by many spaces, not only by the ...

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Java Thread: retained memory analysis

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This article will provide you with a tutorial allowing you to determine how much and where Java heap space is retained from your active application Java threads. A true case study from an Oracle Weblogic 10.0 production environment will be presented in order for you to better understand the analysis process. We will also attempt to demonstrate that excessive garbage ...

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Under the JVM hood – Classloaders

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Classloaders are a low level and often ignored aspect of the Java language among many developers. At ZeroTurnaround , our developers have had to live, breathe, eat, drink and almost get intimate with classloaders to produce the JRebel technology which interacts at a classloader level to provide live runtime class reloading, avoiding lengthy rebuilds/repackaging/redeploying cycles. Here are some of the ...

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Should I use a 32- or a 64-bit JVM?

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This is a question I have faced several times during my career in enterprise software development. Every once in awhile I’ve had to hand out recommendations for configuring a specific new environment. And more often than not, part of the question at hand was related to “Should I use a 32- or a 64-bit JVM”. To be honest, in the ...

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Escaping the JVM heap for memory intensive applications

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If you’ve ever allocated large Java heaps, you know that at some point – typically starting at around 4 GiB – you will start having issues with your garbage collection pauses. I won’t go into detail about why pauses happen in the JVM, but in short it happens when the JVM does full collections and you have a large heap. ...

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Why can’t I turn off the Garbage Collector?

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Let’s start with a quick rewind to the early days of my career as a Java developer. I wanted to eliminate Garbage Collection (GC) pauses from a test that I was conducting. Lo and behold I was annoyed when I discovered that it couldn’t be done. Back then I left the issue for a “design error” and moved on with ...

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Should you trust the default settings in JVM?

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JVMs are considered smart nowadays. Not much configuration is expected – just set the maximum heap to use in the startup scripts and you should be good to go. All other default settings are just fine. Or so some of us mistakenly thought. Actually there is a lot going on during runtime which cannot be automatically adjusted for performance, so ...

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Yammer Metrics, A new way to monitor your application

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When you are running long term applications like web applications, it is good to know some statistics about them, like number of requests served, request durations, or the number active requests. But also some more generic information like the state of your internal collections, how many times some portion of code is being executed, or health checks like database availability, ...

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