title: Database architecture using Redis + Node.js
body: <p>Following some other SO questions, I'm developing a website monitoring application as a pet project with the goal of learning more about Node.js + Redis.</p>
  
  <p>What I have planned is to let users add urls and add them to a Redis <code>SET</code>. Every minute, I get the SET results, do a HTTP Get request and print the response.</p>
  
  <p>This seem to work fine, however, I have a couple of questions:</p>
  
  <ol>
  <li><p>Given that Redis SET does not allow repeated keys (which will save me from doing a request to the same URL), how do I control when a user removes the URL from his account but another user has the same URL? <strong>Can I have an <code>INCR</code> value in the URL key so I know how many users have the URL in their account?</strong></p></li>
  <li><p>Given that I do an HTTP request every minute and I want to use Redis to save the results (response time, up/down, etc), <strong>what's the best way to save all that data in Redis (results from the requests to each url every minute)? Shall I save each response in a unique Redis key?</strong></p></li>
  <li><p>In order to show results to the user in real-time, what's the best way to query the results and parse it in real-time?</p></li>
  </ol>
  
  <p>Thanks for the help.</p>