Hey Tony,<br><br>A while back I exchanged some messages about the tenuring threshold on this list, see:<br><br><a href="http://mail.openjdk.java.net/pipermail/hotspot-gc-use/2008-January/000027.html" target="_blank">http://mail.openjdk.java.net/pipermail/hotspot-gc-use/2008-January/000027.html</a><br>
<br>My MaxTenuringThreshold at the time was set to 30, but if you look at the plots attached to the email thread above, you can see it never went above 16. I had MTT set so high since I had a lot of short-lived data that would get promoted and GC'd when the next tenured area collection ran, which to me meant they were getting promoted too soon. I was using 1.5.0_12 and was always on it, so the change in bit size for the age value wasn't that big of deal, I guess. I was somewhat perplexed at the time as to why the threshold never went above 16 and now I know why. I currently have it set to 4 (along with a modified survivor space size), since I had a lot of unnecessary copying and the premature promotion issues discussed in the above post. <br>
<br>My experience has shown that having a really high MTT leads to a ton of extra copying. Likewise, I'm not sure in what circumstances NeverTenure would be a good idea. The whole point of generational garbage collection is to get junk that sticks around a while out of the hot area of memory, isn't it? Both of these settings seem to indicate that you'ld be better off using non generational GC.<br>
<br>For what it's worth, if I am working with a new application that has gc
problems on a jvm that hasn't been tuned, I would set MTT to 4 with CMS
and see how it worked and iterate from there.<br><br>In Summary, current MTT=4. As to the change impacting performance, I'm not sure since I never ran this particular app on a rev of the JVM that old.<br><br>Jim<br>
<br><br><div class="gmail_quote">On Thu, May 29, 2008 at 4:52 PM, Tony Printezis <<a href="mailto:tony.printezis@sun.com" target="_blank">tony.printezis@sun.com</a>> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
(this is a follow-up to a discussion on the hotspot-gc-dev list)<br>
<br>
We're trying to take a quick poll on what values you use for<br>
MaxTenuringThreshold and whether the decrease in age field size from 5<br>
to 4 bits (from 1.5u6) seemed to have affected the performance of your app.<br>
<br>
This is the thread, if you're interested:<br>
<br>
<a href="http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2008-May/000309.html" target="_blank">http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2008-May/000309.html</a><br>
<br>
Tony, HS GC Group<br>
<br>
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