title: Understanding Eventual Consistency in Cassandra from theory
body: <p>I am just on the way writing my bachelor thesis.
      So therefore I am concerned with Eventually Consistency in theory and how Cassandra applies this theory.
      To understand my problem, consider the following definitions of consistency (as far as I understood):</p>
  
  <ul>
  <li><p><strong>Causal Consistency:</strong></p>
  
  <p>A system provides causal consistency if memory operations that
  potentially are causally related are seen by every node of the system
  in the same order. (wikipedia)</p>
  
  <p>So if a Process A writes a data X into the DB and after that a process B reads this data X and overwrites this with Y, then we say that a Causal Consistency is ensured if B gets X after A on all replicas (resp. nodes).</p></li>
  <li><p><strong>Read-your-write Consistency:</strong></p>
  
  <p>This is a special case of Causal Consistency. Hereby the reading and writing is processed on the same process A. This type of consistency ensures that A will never have an older object of data after the modification.</p></li>
  <li><p><strong>Session Consistency:</strong></p>
  
  <p>In this case a process A accesses the DB in a Session. As long as this Session exists, the system guarantess you a Read-your-write Consistency</p></li>
  <li><p><strong>Monotonic Read Consistency:</strong></p>
  
  <p>If a process gets a specific data object after reading, the system guarantees that a process on every subsequent Read-Access won't get an older data object.</p></li>
  <li><p><strong>Monotonic Write Consistency:</strong></p>
  
  <p>In this case the Write options to the DB will be done serialised whereby the order of the write options results which process came first to write.</p>
  
  <p>Now that are some Consistency options in theory which some or one of them is implemented in the NoSQL-system. But please correct me if I understood something wrong.</p></li>
  </ul>
  
  <blockquote>
    <p><strong>My question is which type of Consistency is provided by CASSANDRA?</strong>
     And how are these Consistencys related to the Rule "R+W>N" respectively "R+W&lt;=N"</p>
  </blockquote>
  
  <pre><code>whereby 
  R=read replica count 
  W=write replica count 
  N=replication factor
  
  I'd really appreciate a quick answer. Thank You!!!
  </code></pre>