caching

WHEN_TO_USE

• When implementing a cache layer (in-memory, Redis, CDN) for an API or service.
• When choosing TTL values or invalidation strategies for cached data.
• When designing cache key schemas to avoid collisions or stale-data bugs.
• When reviewing code that reads from or writes to any cache.
• When debugging stale data, cache stampedes, or inconsistent responses.
• When configuring TanStack Query staleTime/gcTime for client-side caching.

INVALIDATION

• [P0-MUST] Define an invalidation strategy for every cache. Stale data is worse than no cache.
• [P0-MUST] Invalidate caches when the underlying data changes — do not rely solely on TTL expiry.
• [P1-SHOULD] Prefer event-driven invalidation (on write/update/delete) over time-based expiry alone.
• [P1-SHOULD] Use cache versioning (include a version key) when data schemas change.

TTL_GUIDELINES