Step 4: Identify the key issues

Once you have a basic design in mind, focus on the key issues. Identify the bottlenecks and major challenges of the system, and then adjust your design to handle them.

In the TinyURL example, a challenge you might consider is that some URLs are frequently accessed, while others suddenly peak when they go viral on social media. You don't want to hit the database for every request, so you could add a cache layer.