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    Doing class unloading with CMS will often increase the remark pause

    times<br>

    and so is not on by default.  <br>

    <br>

    On 11/5/2011 3:29 PM, Martin Hare Robertson wrote:

    <blockquote

cite="mid:CA+41Qxos87ROt57vanm8PaOiEE2S9XaCc27RjL9S6HBfATmG4Q@mail.gmail.com"

      type="cite">

      <pre wrap="">Hi,

I recently encountered an interesting GC issue with a Tomcat application. I

came up with a simple repro scenario which I posted to StackOverflow:

<a class="moz-txt-link-freetext" href="http://stackoverflow.com/questions/8017193/when-does-the-perm-gen-get-collected">http://stackoverflow.com/questions/8017193/when-does-the-perm-gen-get-collected</a>

To solve this issue I have been encouraged to use

-XX:+CMSClassUnloadingEnabled.

I currently use the following GC configuration.

-XX:+UseMembar

-XX:+UseConcMarkSweepGC

-XX:+UseParNewGC

-XX:CMSInitiatingOccupancyFraction=80

-XX:+UseCMSInitiatingOccupancyOnly

Is enabling CMSClassUnloadingEnabled likely to have a negative perf impact?

If not, why is it disabled by default?

Thanks

Martin

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</pre>

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