How do the per-site cache and Vary headers interact?
PICTURE THIS: HOW TO EXPLAIN IT
Simple meaning
UpdateCacheMiddleware/FetchFromCacheMiddleware store responses keyed by path plus the Vary-derived header values.
WHY — Caching instead of guessing?
Why interviewers care about Caching:
question about Caching.
trade-offs, and what you would actually do on a Python project - not buzzwords.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1UpdateCacheMiddleware/FetchFromCacheMiddleware store responses keyed
by path plus the Vary-derived header values.
- 2If you cache a
page that varies on Cookie but forget Vary, users can receive someone else's personalized HTML.
- 3Never enable the site
cache for authenticated HTML without a careful Vary: Cookie strategy, which often defeats the cache.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
UpdateCacheMiddleware/FetchFromCacheMiddleware store responses keyed by path plus the Vary-derived header values. If you cache a page that varies on Cookie but forget Vary, users can receive someone else's personalized HTML.