title: How does redis claim O(1) time for key lookup?
body: <p>I have a question - lookup of a key value pair in an index - let's say on cassandra or postgres - is typically at around O(logn) </p>
  
  <p>source: <a href="https://github.com/tinkerpop/blueprints/wiki/Graph-Indices" rel="noreferrer">https://github.com/tinkerpop/blueprints/wiki/Graph-Indices</a>. </p>
  
  <p>In the redis documentation it states that runtime complexity is O(1). </p>
  
  <p>Source: <a href="http://redis.io/commands/get" rel="noreferrer">http://redis.io/commands/get</a>
  <a href="http://redis.io/commands/hget" rel="noreferrer">http://redis.io/commands/hget</a></p>
  
  <p>And getting the value of multiple keys is only linear O(m) where m is the number of keys retrieved 
  <a href="http://redis.io/commands/hmget" rel="noreferrer">http://redis.io/commands/hmget</a></p>
  
  <p>How is it possible?</p>