Reducing calls.
WHY CACHE
Fewer requests, faster responses, and resilience when the provider is slow.
WHAT TO CACHE
Data that changes rarely Reference data Anything expensive to fetch
WHAT NOT TO CACHE
Anything that must be current Anything specific to a user, unless keyed properly
WHY THAT SECOND POINT MATTERS
A cache keyed carelessly serves one user's data to another.
WHAT TO INCLUDE IN THE KEY
Everything affecting the result, including the caller.
WHAT CACHE HEADERS PROVIDE
The provider telling you how long a response remains valid.
WHAT TO RESPECT
Those instructions, where given.
WHAT CONDITIONAL REQUESTS PROVIDE
Asking whether something changed, receiving nothing if not.
HOW
Sending a previously received validator with the request.
WHY THAT HELPS
It saves transfer, though not the round trip.
WHAT EXPIRY TO SET WHERE THE PROVIDER GIVES NONE
Short, and based on how stale you can tolerate.
WHAT TO DO WHEN THE PROVIDER IS UNAVAILABLE
Serve stale data, if that is better than failing.
WHAT TO TELL THE USER
That the data may be out of date.
WHAT TO MONITOR
Hit rate, and whether caching is actually helping.
WHAT TO TEST
Behaviour with the cache empty.
