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Technicalstandard
What is a cache, and what could go wrong if your product relies on one?
How to approach it
Define a cache in one sentence, then focus on the product risk: showing users old or wrong data.
How a strong answer opens
“A cache is a fast store of recent results, so you can skip slow work like a database query. The product risk is that it can show users old or wrong data.”
Outline of a strong answer
Try answering out loud for a few minutes before you open this.
- Definition: a fast store of recent results so you skip slow work
- Examples: browser cache, CDN, in-memory cache in front of a database
- Benefit: speed and lower cost
- Risk: stale data, such as a price or stock level that has changed
- Risk: a cache failure suddenly sends all traffic to the database
- PM decision: which data can be a little stale and which never can
Where this question usually goes wrong
Presenting caches as pure speed wins without mentioning stale data or what happens when the cache fails.
Learn the method
Technical trade-offs in Module 6, Technical for PMs.
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