Caching

A URL shortener turns https://example.com/a/very/long/path?campaign=autumn into something like sho.rt/6ZY3LCH, and sends anyone who opens the short link to the …

A URL shortener's redirect endpoint, GET /r/{code}, looks purely read-heavy — billions of redirects against a handful of short codes created per second. But eve…

A 4-node session cache scales to 5 nodes to handle more traffic. With hash(key) % N, that single node addition changes almost every key's target node, and the c…

A shopping cart must remember items, so the product cannot be literally stateless. The useful design question is where that state lives. Keep the cart inside on…

A dashboard can look “fast” while users still wait, and a load test can report huge requests-per-second while p99 checkout times explode. Latency is how long on…

Checkout slows while product pages remain healthy. CPU is moderate, but the orders table shows rising lock waits and writes queue behind one hot index. Adding a…

A product page is easy to cache until a price changes: the CDN still has the old response, one app instance has an older in-process value, and Redis has already…

A product page's cache key expires at 2:00:00pm. In the same instant, 5,000 concurrent requests check the cache, all get a miss, and all 5,000 independently que…