Thursday, July 4, 2013

Java : Garbage Collection in Java (4)

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The Problem: Large heaps mean Large Pause Times

The Concurrent Mark and Sweep (CMS) collector is the currently recommended low pause collector, but unfortunately its pause times scale with the amount of live objects in its tenured region. This means that whilst its relatively easy to get short GC Pauses with smaller heaps, but once you start using heaps in the 10s or 100s of Gigabytes the times start to ramp up.

CMS also doesn't "defrag" its heap so at some point in time you'll get a concurrent mode failure (CMF), triggering a full gc. Once you get into this full gc scenario you can expect a pause in the timeframe of roughly 1 second per Gigabyte of live objects. With CMS your 100GB heap can be a 1.5 minute GC Pause ticking time bomb waiting to happen ...


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