Just found two nice blog entries by Chaotic Java which explain nicely how Java Garbage Collection works. Might be still too much if you have never dealt with the topic before, but good reading for the others.
Enjoy reading.
Category Archives: Java
The Argument about the Curly Brackets
When you talk about code styleguides, you often talk about basic formatting. This means you probably already fought the holy war over the curly brackets {} and where to put them.
Of course, the next line is the only right place. A curly bracket is a hermit and does not like to be put next to any other character… :)
What is your opinion?
Cartoon courtesy of Geek and Poke under CC-BY-ND-2.0
XLT – Garbage Collector details visualized
Today we want to give you a small preview of an upcoming XLT feature. Most of you probably know that XLT features agent statistics. These statistics help you to keep an eye on the health of the test execution engines (agents) to ensure that you do not influence the test results by providing insufficient hardware or by applying no or incorrect settings.
Most modern programming languages are virtual machine based and these machines have knobs you can turn to adjust their behavior according to your requirements. XLT runs on Java and so all the things you might have already learnt from tuning your Java-based servers apply to XLT as well. If you do not have experience in tuning your Java-based servers, you will learn a lot that can be applied to your servers and help you to increase performance.
Continue reading XLT – Garbage Collector details visualized
What is the state of the G1 Garbage Collector?
Because I do not know what is the current state of the Java G1 Garbage Collector, I decided to try G1 with JDK6u20. Somehow I was disappointed because after a short moment of predictable GC performance, the entire VM stopped and some major collection was running. You can easily see that in the charts of that run. Right around 20:09:45, the threads were stopped and the entire VM behaved ugly.
So, the G1 is not yet ready for production, of course nobody stated that it is ready for production. If I read the release notes of JDK6u21 correctly, it delivers plenty of G1 changes, so I might try that soon.
Some nice reading about HBase
If you want to stay in touch with cutting-edge technology in terms of scalability of databases, high traffic sites, and large storage volumes, you should read these two articles on the new hstack.org blog.
Cosmin Lehene wrote two excellent articles on Adobe’s experiences with HBase: Why we’re using HBase: Part 1 and Why we’re using HBase: Part 2. Adobe needed a generic, real-time, structured data storage and processing system that could handle any data volume, with access times under 50ms, with no downtime and no data loss. The article goes into great detail about their experiences with HBase and their evaluation process, providing a “well reasoned impartial use case from a commercial user”. It talks about failure handling, availability, write performance, read performance, random reads, sequential scans, and consistency.
(via High Scalability)
Ein empfehlenswertes Blog – Java Concurrency
Jeremy Manson schreibt in seinem Blog über Java Concurrency und interessante Dinge, die in einer JVM passieren, aber meist niemanden interessieren.
Jeremy ist bei Google angestellt und in viele JSR-Prozesse rund um das JDK involviert.
Java-GC unter die Haube schauen
Diese Optionen für das JDK6 sollte man kennen, wenn man dem Garbage Collector bei der Arbeit zusehen will. Speziell für das GC-Tuning sind diese Optionen unerlässlich:
Details zu den Optionen und zur Auswertung kann man unter GC Tuning oder in der Liste der JDK-Optionen finden.
Java zeichnet langsam unter Windows
Wer das Problem hat, dass seine Java-Anwendung – zum Beispiel Freemind oder Visual GC – unter Windows wie in Zeitlupe die Fensterinhalte malt, der sollte mal diesen Parameter ausprobieren:
-Dsun.java2d.noddraw=true
Mehr dazu findet sich bei Sun unter Graphics Performance Improvements.
Singletons auf die faule Art
Wir hatten heute eine kurze Diskussion über Singletons und die Art und Weise ihrer Erzeugung, speziell wenn man sie faul (lazy) erzeugen möchte. Die Wikipedia hat dazu diesen schönen Eintrag – On Demand Holder Idiom:
In software engineering, the Initialization on Demand Holder idiom (design pattern) is a lazy-loaded singleton. The idiom can be implemented in both single-threaded/serial and concurrent environments, but care must be taken to correctly implement the idiom under concurrent conditions.
Ganz besondern wichtig ist die Erklärung, warum Lazy in diesem Fall so und nicht anders funktioniert:
The implementation relies on the well-specified initialization phase of execution within the Java Virtual Machine (JVM); see section 12.4 of Java Language Specification (JLS) for details.
When the class Something is loaded by the JVM, the class goes through initialization. Since the class does not have any static variables to initialize, the initialization completes trivially. The static class definition LazyHolder within it is not initialized until the JVM determines that LazyHolder must be executed. The static class LazyHolder is only executed when the static method getInstance is invoked on the class Something, and the first time this happens the JVM will load and initialize the LazyHolder class.
War das Internet kurz vor Offline?
Netter Artikel bei Heise Online, auch wenn man den Inhalt nur schwer versteht… selbst als Informatiker hat man da seine Probleme. Angeblich soll das Internet kurz vor Offline in weiten Teilen gestanden haben, weil ein Bedienfehler und mehrere Softwarefehler zusammentrafen.
Routing und Cisco-Zeugs sind eh nicht jedermanns Sache… übrigens bin ich gegen Firmenmonopole. Cisco beherrscht das Netz durch sein Ausstattungsmonopol. Die meisten grossen Internetprovider und Backbone-Betreiber setzen auf Cisco.
Hoffen wir mal, dass Cisco ausreichend bezahlte Mitarbeiter hat und/oder ausreichend Codereviews macht. Sonst ist es vorprogrammiert, dass mal jemand eine Hintertür für seine Zeit nach Cisco legt.