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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Update of "PerformanceTuning" by LarsGeorge
Date Fri, 25 Sep 2009 07:46:05 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Hadoop Wiki" for change notification.

The "PerformanceTuning" page has been changed by LarsGeorge:
http://wiki.apache.org/hadoop/PerformanceTuning?action=diff&rev1=5&rev2=6

  
  You can save a lot of time by enabling JVM re-use on MR jobs. In the JobTracker, or the
Job itself, set {{{mapred.job.reuse.jvm.num.tasks}}} to the number of times to reuse a JVM
''for the same map or reduce transform''  -or to -1 to reuse without limits. This reduces
JVM startup/teardown times. 
  
- The more copies of a block there is, the more places there are to schedule work on the same
host as the block, so eliminating the need to copy the block over the network. Set the {{block.replication.factor}}
on files to be more than the default (usually 3) if you want to make it accessible in more
spaces. 
+ The more copies of a block there is, the more places there are to schedule work on the same
host as the block, so eliminating the need to copy the block over the network. Set the {{{block.replication.factor}}}
on files to be more than the default (usually 3) if you want to make it accessible in more
spaces. 
  
  == HBase Performance tips ==
  

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