Cache invalidation and expiration

Set value and expiry atomically when the command supports it; SET followed by EXPIRE has a crash window. Choose TTL from acceptable staleness and add jitter when synchronized expirations would create a herd.

Cache-aside reads can race with writes and slow refreshes. Define invalidation/versioning and whether stale serving is allowed; deleting a key after a write is not a universal proof against old data being refilled later.

Use bounded negative caching for valid not-found results, keyed by authorization scope. Collapse repeated loads and bound origin concurrency. A cache is only optional if the fallback can survive its absence.