Twitter uses Snowflakes, simialr to FB and other services. They scale better than manual ID range allocation and don't entirely behave like auto-increment. The

Twitter uses Snowflakes, simialr to FB and other services. They scale better than manual ID range allocation and don't entirely behave like auto-increment. The big part is that it can contain gaps. So there is no way to tell if an ID doesn't exist because you lack access or because it was skipped over.