When we reach for it
Caching expensive reads, holding sessions and rate-limit counters, and coordinating background work. It does a small number of things and does them at a latency nothing on disk can match.
Redis
An in-memory data store for caching, rate limiting, sessions and queues, where the whole point is that an answer arrives in under a millisecond.
What we reach for first
When we would argue against it
It is not a database of record unless it has been configured as one deliberately, and we do not let it become the only place a fact exists. A cache with no invalidation strategy is a bug with a delay on it.
What it looks like in delivery
Every cached key gets an expiry and a documented invalidation path before it goes in. We would rather serve a slower correct answer than a fast stale one, and we make the trade explicit rather than discovering it in support.
Where this appears on the site
Published work that names it
Derived from the stacks published on those pages, not written here — so this list cannot claim something the page it points at does not say.
Also in data and storage
Working in Redis?
Tell us what it is running, what it costs you today, and what you need it to do next. A senior engineer will tell you what we would keep and what we would change.