[jboss-user] [Performance Tuning] - Re: Options for CMS and G1 Collectors

[Peter Johnson]

Peter Johnson [https://community.jboss.org/people/peterj] created the discussion

"Re: Options for CMS and G1 Collectors"

To view the discussion, visit: https://community.jboss.org/message/722530#722530

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>>I thoguht that it would be a good idea to promote more objects to tenure and take advantage of the CMS collector.

Actually, this is a bad idea based on testing that i haved done. Two reasons:

1) The pauses during CMS and G1 collections (yes, there are pauses - two of them) are about as long as the pause caused by minor collection.

2) While CMS and G1 run, they are using up one entire processor/core at 100% because they are memory and processor intensive. You want those collectors to run as rarely as possible. If you tenure every object that lives through a minor collection, then you are going to run CMS/G1 more often and thus will more often lose the use of a core to process business requests.

See this white paper:
Java Garbage Collection Performance Analysis 201
at  http://www.cmg.org/cgi-bin/search.cgi?q=java+peter+johnson&x=30&y=10 http://www.cmg.org/cgi-bin/search.cgi?q=java+peter+johnson&x=30&y=10
(I worked with a beta version of G1, so take the stability warnings with a grain of salt)
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