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From Apache Wiki <>
Subject [Cassandra Wiki] Update of "ReadRepair" by JonathanEllis
Date Mon, 25 Jul 2011 18:47:56 GMT
Dear Wiki user,

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The "ReadRepair" page has been changed by JonathanEllis:

  This means that in almost all cases, at most the first instance of a query will return old
- One special case to consider: when doing range scans at !ConsistencyLevel ONE, read repair
is not done at all - neither before returning nor as a background thread.  This is especially
relevant for the built-in Hadoop support.  By default it uses !ConsistencyLevel ONE and does
range scans through the column family.
+ Range scans are not per-key and do not do read repair.  (A range scan at CL > ONE *will*
reconcile differences in replicas required to achive the given CL, but extra replicas are
not compared in the background.)

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