Caching

Choose cache duration from the user experience your product promises, not from an assumption that upstream data is instant.

Record retrieval time and cache state. If you serve stale data during a transient failure, make that policy explicit and bounded.

Model time explicitly

Keep at least three values separate: when the data was retrieved, how long it is considered fresh, and the maximum age at which your application may still serve it. “Cached” alone is not enough to explain what a user is seeing.

Coalesce repeated reads

When several workers request the same inventory or market observation, let one bounded refresh own the upstream call while the others use the current snapshot or wait within their own deadlines. Coordination must expire safely if the owner fails.

Preserve outcome meaning

A failed refresh does not erase the last successful value. Store the current accessibility or refresh outcome beside the prior snapshot, and label stale data in user-facing surfaces. Never convert private, missing, or transiently unavailable data into an empty successful response.

Review Synchronize inventory data and Retries & timeouts together; caching cannot make an unbounded retry loop safe.