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From Apache Wiki <>
Subject [Cassandra Wiki] Update of "API" by TylerHobbs
Date Fri, 08 Apr 2011 15:40:24 GMT
Dear Wiki user,

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

The "API" page has been changed by TylerHobbs.
The comment on this change is: ConsistencyLevel ZERO doesn't exist in 0.7.


  ==== Write ====
  ||'''Level''' ||'''Behavior''' ||
- ||`ZERO` ||Ensure nothing. A write happens asynchronously in background. Until [[|CASSANDRA-685]]
is fixed: If too many of these queue up, buffers will explode and bad things will happen.
  ||`ANY` ||Ensure that the write has been written to at least 1 node, including HintedHandoff
recipients. ||
  ||`ONE` ||Ensure that the write has been written to at least 1 replica's commit log and
memory table before responding to the client. ||
  ||`QUORUM` ||Ensure that the write has been written to `N / 2 + 1` replicas before responding
to the client. ||
@@ -44, +43 @@

  ==== Read ====
  ||'''Level''' ||'''Behavior''' ||
- ||`ZERO` ||Not supported, because it doesn't make sense. ||
  ||`ANY` ||Not supported. You probably want ONE instead. ||
  ||`ONE` ||Will return the record returned by the first replica to respond. A consistency
check is always done in a background thread to fix any consistency issues when `ConsistencyLevel.ONE`
is used. This means subsequent calls will have correct data even if the initial read gets
an older value.  (This is called ReadRepair) ||
  ||`QUORUM` ||Will query all replicas and return the record with the most recent timestamp
once it has at least a majority of replicas (`N / 2 + 1`) reported.  Again, the remaining
replicas will be checked in the background. ||

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