Don't ship w/ icms enabled by default
-------------------------------------

                 Key: HBASE-4714
                 URL: https://issues.apache.org/jira/browse/HBASE-4714
             Project: HBase
          Issue Type: Task
            Reporter: stack


"Incremental CMS (iCMS) was written for a specific use case - 1 or 2 hardware
threads where concurrent activity by CMS would look like a STW (if
only 1 hardware thread) or a high tax on the cpu cycles (2 hardware
threads).   It has a higher overhead and also is less efficient in terms
of identifying garbage.  The latter is because iCMS spreads out the
concurrent work so that objects that it has identified as live earlier
may actually be dead when the dead objects are swept up.  It's
worth testing with regular CMS instead of iCMS."

>From recent hotspot mailing list message.

Rare is the case where we run on systems of 1 or 2 hardware threads (other than 
fellows laptops and there the above likely doesn't matter).

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