Tag Archives: tuning

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.
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Softreferenzen gehen jederzeit

Softreferenzen (soft references) in Java sind eine tolle Sache, denn es lassen sich tolle Caches und Notfallszenarien damit bauen. Was kaum jemand weiß, dass Softreferenzen nicht nur im Falle von akuter Speicherknappheit freigegeben werden, sondern durchaus auch früher. Letzteres kann zu unerwarteten Nebenwirkungen führen, speziell mit Blick auf Caching.

Soft references are kept alive longer in the server virtual machine than in the client. The rate of clearing can be controlled with the command line option -XX:SoftRefLRUPolicyMSPerMB=<N>, which specifies the number of milliseconds a soft reference will be kept alive (once it is no longer strongly reachable) for each megabyte of free space in the heap.

The default value is 1000 ms per megabyte, which means that a soft reference will survive (after the last strong reference to the object has been collected) for 1 second for each megabyte of free space in the heap. Note that this is an approximate figure since soft references are cleared only during garbage collection, which may occur sporadically.

Quelle: JDK 6 Garbage Collection Tuning Guide

Nachtrag: Erwähnenswert ist auch dieser Blogeintrag von Jeremy Manson.