[Cassandra Wiki] Update of "ReadRepair" by JonathanEllis

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The "ReadRepair" page has been changed by JonathanEllis.
http://wiki.apache.org/cassandra/ReadRepair?action=diff&rev1=1&rev2=2

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- Read repair means that when a query is made against a given key, we perform that query against all the replicas of the key.  If a low !ConsistencyLevel was specified, this is done in the background after returning the data from the closest replica to the client; otherwise, it is done before returning the data.
+ Read repair means that when a query is made against a given key, we perform that query against all the replicas of the key and push the most recent version to any out-of-date replicas.  If a low !ConsistencyLevel was specified, this is done in the background after returning the data from the closest replica to the client; otherwise, it is done before returning the data.
+ 
+ (To reduce the impact on the network, only the closest replica to the coordinator node actually sends the full result set; the others send hashes.)
  
  This means that in almost all cases, at most the first instance of a query will return old data.