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copied!<p>The break-up of the line is as followd:</p> <p><code>1885.85</code> - this in seconds is the amount of time the JVM has been running, so around 31 minutes or so in your case at which point the GC took place.</p> <p><code>[GC</code> - states a GC occured at this point in time. This is a Partial GC, sometimes it will show <code>Full GC</code></p> <p>Now, the Total Heap available for the JVM = Young + Old</p> <p><code>[PSYoungGen:742996K->64359K(761472K)</code> - represents the Parallel Scavenging Collector in the Young generation (which is one of the many types of GC collectors available in the JVM). </p> <p>The memory freed by GC is always of the pattern </p> <pre><code>x->y(z) </code></pre> <blockquote> <p>x is the initial memory before GC, y is the memory after GC, z is the total memory allowed for that area in the JVM</p> </blockquote> <p>so in your example, <code>742996K->64359K(761472K)</code> - the total Young size is 761Mb, and when it reached 742 Mb a collection took place, and it cleared down to 64.3Mb i.e. it cleared up 678 Mb</p> <pre><code>2509583K->1832973K(4116928K) </code></pre> <p>Here the total heap memory is represented. So out of a total possible heap of 4.1 Gb, when the GC took place, it had filled 2.5 Gb and it has come down to 1.83 Gb - again the same 678 Mb is what got cleared.</p> <pre><code>0.1453610 secs] </code></pre> <p>This entire operation took 0.1453610 seconds</p> <pre><code>[Times: user=0.31 sys=0.00, real=0.14 secs] </code></pre> <p>shows the break-up of <a href="https://stackoverflow.com/questions/556405/what-do-real-user-and-sys-mean-in-the-output-of-time1">user, system and real times</a> taken.</p> <p>This is just one line - you would be looking for a pattern esp one that says <code>Full GC</code> in it And use a log analyzer like <a href="http://jojovedder.blogspot.com/2009/06/slow-weblogic-part-6-jvm-heap-analysis.html" rel="nofollow noreferrer">GCViewer</a> for showing you throughput and other good stuff.</p> <p>Also read the <a href="http://java.sun.com/javase/technologies/hotspot/gc/gc_tuning_6.html" rel="nofollow noreferrer">docs from Sun</a> to get the basics.</p> <p><strong>Further reading:</strong></p> <p><a href="http://sujitpal.blogspot.com/2006/08/charting-jvm-garbage-collection.html" rel="nofollow noreferrer">http://sujitpal.blogspot.com/2006/08/charting-jvm-garbage-collection.html</a></p> <p><a href="https://stackoverflow.com/questions/895444/java-garbage-collection-log-messages">Java Garbage Collection Log messages</a></p>

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