title: How to create unique row ID in sharded databases?
body: <p>In a non-sharded DB, I could just use auto-increment to generate a unique ID to reference a specific row.</p>
  
  <p>I want to shard my DB, say into 12 shards. Now when I insert into a specific shard, the auto-increment ID is no longer unique.</p>
  
  <p>Would like to hear anyone's experience in dealing with this problem. </p>