title: Redis versus Cassandra(Bigtable data model)
body: <p>Suppose I need to do the following operations intensively:<br>
  <code>put(key, value)</code><br>
  where value is a map of &lt;column name, column value&gt;.<br>
  I havn’t known NoSQL for long, what I know is that both Cassandra insert(which conform the api defined in Bigtable paper) and Redis “HSET” command could do that. But what’s the pros and cons of both way? Any performance and scalability difference there?</p>
  
  <p>EDIT : </p>
  
  <p>My requirement is something like an IM server --- I need to store session data , and I want all of them to be in memory so that low latency can be easily achieved. The session last for at most 2 hours. No consistency requirement to consider yet. And disk is only for fail-over. Lost of data is not terrible. All i need is lower latency. Operations per second --- the more, the better.</p>