GO TO A SECTION

↑ ↓ to navigate · Enter to openExplore all sections →
FDEInterviews logo
← System Design & Production Engineering / 43
hardOpenAIVercelRetool

You add a cache in front of an LLM endpoint at a customer. Walk through invalidation, the stampede, and what's safe to cache.

Caching LLM output looks like free latency and cost savings until a cache key collides across tenants or a popular key expires under load and stampedes your model. The senior answer is mostly about what you refuse to cache.

Updated Aug 2026 · Grounded in real Forward Deployed Engineer interview loops and written to a senior-engineer editorial bar.

Caching LLM output looks like free latency and cost savings until a cache key collides across tenants or a popular key expires under load and stampedes your model. The senior answer is mostly about what you refuse to cache.

20 answers per topic instead of 10, plus saved progress and bookmarks · no cardor unlock all 548 remaining answers · ₹2,000 / $25

Every answer, concept and course, every paper breakdown, all published video lessons, hands-on FDE Lab missions, Premium PDF guides and companion files, the full practice-test bank and work-sample downloads. Referral Premium excludes guide PDFs and their companion files.

6 months · One payment · No auto-renewal

Study alongside free video lessons.

Course lessons in this topic

Keep practising

Next in this trackA service you deployed at a customer corrupts a record intermittently under concurrency. How do you find it and fix it?PremiumNext in this trackDesign the integration API a customer's engineers can adopt without it breaking on them: REST vs GraphQL, versioning, pagination.PremiumNext in this trackHow do you design a customer deployment so their team can run it without you, and you make yourself obsolete?Premium
FEDITOR'S NOTE

The differentiating moves are: cache keys must include every input that changes the answer (model, version, full prompt, retrieved context, tenant), and stampede protection via single-flight/locking on miss. A weak answer caches naively and leaks one tenant's answer to another or serves stale results after a prompt change. Probe with 'the customer updated their knowledge base, now what's in the cache is wrong' to test invalidation by versioned key vs TTL.

DISCUSSION · 0

No comments yet — be the first to share your approach.