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From Apache Wiki <wikidi...@apache.org>
Subject [Cassandra Wiki] Update of "VirtualNodes/Balance" by JonathanEllis
Date Thu, 02 Aug 2012 18:29:28 GMT
Dear Wiki user,

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The "VirtualNodes/Balance" page has been changed by JonathanEllis:
http://wiki.apache.org/cassandra/VirtualNodes/Balance?action=diff&rev1=6&rev2=7

  
   * Shuffling will entail moving a ''lot'' of data around the cluster and so has the potential
to consume a lot of disk and network I/O, and to take a considerable amount of time.  For
this to be an online operation, the shuffle will need to operate on a lower priority basis
to other streaming operations, and should be expected to take days or weeks to complete.
  
+  * Corollary: shuffling should tell the operator what vnodes it plans to move where, and
report progress whenever one completes successfully.  This will allow recovering from an interrupted
shuffle, if necessary.
+ 
+  * Shuffling can be sped up by parallelizing such that each node has one vnode moving to
or from it at a time.  With appropriate stream throttling this should be better than just
one vnode at a time cluster-wide.
+ 
  === Nodes / Cluster ===
  The most straightforward method of effecting ownership is a token move (i.e. relocating
a range from one node to another).  Exposing this with JMX would allow implementing all of
the required operations client-side.
  

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