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copied!<p>An Oracle guy wrote a <a href="https://blogs.oracle.com/poonam/entry/understanding_g1_gc_logs" rel="nofollow">blog post</a> that explains every part of the GC log. I found it very useful. </p> <p>Here is a quote from the blog.</p> <blockquote> <p>0.522: [GC pause (young), 0.15877971 secs]</p> <p>This is the highest level information telling us that it is an Evacuation Pause that started at 0.522 secs from the start of the process, in which all the regions being evacuated are Young i.e. Eden and Survivor regions. This collection took 0.15877971 secs to finish.</p> <p>Evacuation Pauses can be mixed as well. In which case the set of regions selected include all of the young regions as well as some old regions.</p> <p>1.730: [GC pause (mixed), 0.32714353 secs]</p> <p>Let's take a look at all the sub-tasks performed in this Evacuation Pause.</p> <p>[Parallel Time: 157.1 ms]</p> <p>Parallel Time is the total elapsed time spent by all the parallel GC worker threads. The following lines correspond to the parallel tasks performed by these worker threads in this total parallel time, which in this case is 157.1 ms.</p> <p>[GC Worker Start (ms): 522.1 522.2 522.2 522.2 Avg: 522.2, Min: 522.1, Max: 522.2, Diff: 0.1]</p> <p>The first line tells us the start time of each of the worker thread in milliseconds. The start times are ordered with respect to the worker thread ids – thread 0 started at 522.1ms and thread 1 started at 522.2ms from the start of the process. The second line tells the Avg, Min, Max and Diff of the start times of all of the worker threads.</p> </blockquote>

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