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List: jboss-user
Subject: [jboss-user] [Performance Tuning] - Re: Full Garbage Collection
From: Peter Johnson <do-not-reply () jboss ! com>
Date: 2010-11-30 18:24:06
Message-ID: 2-571975-3-77742-1290176769917-2-573717-3-2143-1291141439685.jivesbs.jivemailuser () http://community ! jboss ! org
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Peter Johnson [http://community.jboss.org/people/peterj] created the discussion
"Re: Full Garbage Collection every few seconds – GC frees very little memory \
(JBoss 4.2.3 with JDK 1.5.0 64-bit)"
To view the discussion, visit: http://community.jboss.org/message/573717#573717
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> If I had a memory leak, wouldn't I always get an OutOfMemoryError eventually? \
> As I wrote on the first post, the JVM is never throwing one.
That is true, but continual full GCs means that the app's working set size is a very \
large percentage of the heap and that you have sized the heap too small. And when \
you use the CMS collector you need to size the heap even larger, if you don't then \
you run into the possibility of the CMS collector not being able to free up memory in \
a timely fashion, in which case a very expensive (time-wise) stop-the-world \
collection takes place. Right-sizing the heap usually takes a lot of GC monitoring \
and experimentation to get right, though the easiest way is to allocate a very large \
heap to begin with (like Jimy Liu suggested) and monitor that, then you can usually \
come up with a decent heap size.
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17px; font-weight: normal;"> Re: Full Garbage Collection every few seconds – \
GC frees very little memory (JBoss 4.2.3 with JDK 1.5.0 64-bit) </h3>
<span style="margin-bottom: 10px;">
created by <a href="http://community.jboss.org/people/peterj">Peter Johnson</a> \
in <i>Performance Tuning</i> - <a \
href="http://community.jboss.org/message/573717#573717">View the full discussion</a> \
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<div class="jive-rendered-content"><blockquote class="jive-quote">If I had a memory \
leak, wouldn't I always get an OutOfMemoryError  eventually?  As I wrote on \
the first post, the JVM is never throwing  one.</blockquote><p>That is true, but \
continual full GCs means that the app's working set size is a very large percentage \
of the heap and that you have sized the heap too small.  And when you use the \
CMS collector you need to size the heap even larger, if you don't then you run into \
the possibility of the CMS collector not being able to free up memory in a timely \
fashion, in which case a very expensive (time-wise) stop-the-world collection takes \
place. Right-sizing the heap usually takes a lot of GC monitoring and experimentation \
to get right, though the easiest way is to allocate a very large heap to begin with \
(like Jimy Liu suggested) and monitor that, then you can usually come up with a \
decent heap size.</p></div>
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<p style="margin: 0;">Reply to this message by <a \
href="http://community.jboss.org/message/573717#573717">going to Community</a></p> \
<p style="margin: 0;">Start a new discussion in Performance Tuning at <a \
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