[Hadoop Wiki] Trivial Update of "PerformanceTuning" by stack

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The following page has been changed by stack:
http://wiki.apache.org/hadoop/PerformanceTuning

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   * Use a 64-bit platform, and a 64-bit JVM.
   * Your clients might need tuning: [http://ryantwopointoh.blogspot.com/2009/01/performance-of-hbase-importing.html]
   * Make sure that the command {{{java}}} implies {{{-server}}} on your machines, or else you will have to explicitly enable it.
+  * Are you swapping?  JVMs hate swapping.  Adjusting [http://www.sollers.ca/blog/2008/swappiness/ swappiness] may help.
+  * By default, each regionserver puts up 10 listeners only.  Up it if you have measurable traffic (See hbase.regionserver.handler.count in hbase-default.xml).
  
  == HBase JVM and GC ==
  
@@ -30, +32 @@

  To enable, in hbase-env.sh add: {{{
  export HBASE_OPTS="-XX:+UseConcMarkSweepGC -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCTimeStamps -Xloggc:/home/hadoop/hbase/logs/gc-hbase.log"
  }}}
+ 
+ (As of 0.20.0 HBase, CMS is enabled by default).
  
  Adjust the log directory to wherever you log.