Design Twitter for millions of users

What data will you store for each tweet? (tweet ID, user ID, timestamp, text, media link, etc.)

How will you design for billions of tweets, millions of users, and high fan-out (e.g., celebrities with millions of followers)?

How will you index tweets and store user timelines? (e.g., in separate timeline storage or as pointers to tweet objects?)

What will you cache (timelines? tweet metadata?) and where (e.g., Redis)?