Design a URL Shortener

Design a URL Shortener

Step 1 of 11

reads/s500writes/s5

A hundred million links, and 500 reads for every 5 writes. The read path is the design.

The Idea

Take a long URL, hand back a short key, and redirect every later hit on that key. Assume 100 million links and 500 redirects a second against 5 writes — read-heavy, and every read is one exact-key lookup.

Real-World Example

A cloakroom ticket. The number you are given says nothing about your coat; the desk's ledger is the only thing that connects the two, and it is read far more often than it is written.

The Tradeoff

A base62 counter gives the shortest collision-free keys and leaks how many links exist, because one shared sequence hands them out in order. Random keys hide that and need a uniqueness check on every write. Redirect with 302: a 301 is cached by the browser forever, and your click counts stop arriving.

Your turn

Put the steps in the right order.

1. 1Answer with 302 to the long URL and publish a click event↑↓
2. 2Generate a short key and confirm no row already holds it↑↓
3. 3On a redirect, read the cache first and fall back to the store↑↓
4. 4Write key to long URL, then return the short link↑↓

Check order

Mini quiz

1 / 3

The redirect is a 302 rather than a 301 because:

• A302 is faster to parse
• BA permanent redirect is cached by the browser, so later clicks never reach you
• C301 is not valid for short links
• D302 compresses better over HTTP/2