Lesson 3: Caching answers and keeping them fresh
27 min read·13 Oct 2026
Module 12 · Lesson 3 · About 50 minutes · Needs: Module 5 Lesson 4 (upserts, deletes, blue/green swaps), Module 4 Lesson 4 (model versions), Module 7 Lesson 3 (the cache key)
The situation
On Wednesday 7 October Kwame replayed a customer's question through the staging service: "how long will a repair booked this week take". The answer, from the repair centre notice, said 2 extra working days, and Owen asked for answers like it to be cached: the same questions arrive all day, and each costs a model call.
On Thursday Hannah's update batch changed that notice to 3 days and withdrew bulletin SB-114. On Friday Ellie asks the same question. Grace wants caching that saves money without serving Wednesday's answer. The Hollin data and times are simulated.