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From: Apache Wiki <wikidiffs@apache.org>
To: cassandra-commits@incubator.apache.org
Date: Tue, 25 Aug 2009 00:15:01 -0000
Message-ID: <20090825001501.6377.18936@eos.apache.org>
Subject: [Cassandra Wiki] Update of "API" by JoeStump

Dear Wiki user,

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The following page has been changed by JoeStump:
http://wiki.apache.org/cassandra/API

The comment on the change is:
Added notes on ConsistencyLevel.

------------------------------------------------------------------------------
   UnavailableException:: Not all the replicas required could be created and/or read.
   TApplicationException:: Internal server error.
  
+ == Structures ==
+ 
+ === ConsistencyLevel ===
+ 
+ The `ConsistencyLevel` is an `enum` that controls both read and write behavior based on `<ReplicationFactor>` in your `storage-conf.xml`. The different consistency levels have different meanings, depending on if you're doing a write or read operation.
+ 
+ ==== Write ====
+ 
+ ||'''Level'''||'''Behavior'''||
+ ||`ZERO`||Only ensure that the write has been written to the commit log.||
+ ||`ONE`||Ensure that the write has been written to at least 1 node's commit log and memory table.||
+ ||`QUORUM`||Ensure that the write has been written to `<ReplicationFactor> / 2 + 1` nodes.||
+ ||`ALL`||Ensure that the write is written to `<ReplicationFactor>` nodes.||
+ 
+ ==== Read ====
+ 
+ ||'''Level'''||'''Behavior'''||
+ ||`ZERO`||Not supported.||
+ ||`ONE`||Will return the record returned by the first node to respond. A background thread is always fired off to fix any consistency issues when `ConsistencyLevel.ONE` is used. This means subsequent calls will have correct data while the initial read may not.||
+ ||`QUORUM`||Will query all storage nodes and return the record that is prevailing in consistency. For instance, if `foo = 1` on nodes A and B, while `foo = 2` on node C then the prevailing consistency is `foo = 1`. A background thread will be fired off to fix consistency issues.||
+ ||`ALL`||Not supported.||
+