Practice — Design a URL Shortener (bit.ly / TinyURL) (6 questions)

An interviewer gives you these assumptions for a URL shortener: 500 million new links per month, a 200:1 read/write ratio, links must be retained for 10 years, and each stored record averages 500 bytes.

1. Compute average writes/s and reads/s, and a reasonable peak figure.
2. Compute total storage after 10 years.
3. Using the 80/20 rule, size a cache that holds the hottest 20% of URLs requested in one day. Is one Redis node enough?

Your URL shortener uses codes drawn from [a-z A-Z 0-9] — 62 characters.

How many unique URLs can a 6-character code hold, and at 1,000 new URLs per second, how long until the keyspace runs out?

Show the arithmetic, and say whether you'd launch with 6 or 7 characters.