Third Time’s the Cache, No More

Caching is a big part of how Cloudflare CDN makes the Internet faster and more reliable. When a visitor to a customer’s website requests an asset, we retrieve it from the customer’s origin server. After that first request, in many cases we cache that asset. Whenever anyone requests it again, we can serve it from one of our data centers close to them, dramatically speeding up load times.

Did you notice the small caveat? We cache after the first request in many cases, not all. One notable exception since 2010 up until now: requests with query strings. When a request came with a query string (think https://example.com/image.jpg?width=500; the ?width=500 is the query string), we needed to see it a whole three times before we would cache it on our default cache level. Weird!

This is a short tale of that strange exception, why we thought we needed it, and how, more than ten years later, we showed ourselves that we didn’t.

Two MISSes too many

To see the exception in action, here’s a command we ran a couple weeks ago. It requests an image hosted on example.com five times and prints each response’s CF-Cache-Status header. Continue reading