title: How to implement "trigger" for redis datastore?
body: <p>I have a program, which will poll on a certain key from the redis datastore, and do something when the value satisfies a certain condition.</p>
  
  <p>However, I think periodically polling on redis is quite inefficient, I'm wondering if there is a "trigger" mechanism for redis, when the value changes and satisfies the condition, the trigger will be called. The trigger might be a RPC function, or an HTTP msg, or something else, so that I don't need to poll on it any more, just like the difference between poll and interrupt.</p>
  
  <p>Is this possible?</p>