Cache

# Cache-aside

# Hot Key

Cache invalidation is a consistency protocol

• use versioned cache entries or conditional writes so that an older in-flight write can not overwrite a newer value.

# Production improvements

# Single-flight/request coalescing

one in-flight refresh per key, with a bounded number of waiters.

# TTL jitter

spread expiration times to prevent synchronized expiry.

# Stale-while-revalidate

serve stale data only where the freshness policy permits it.

# Negative caching

cache selected “not found” results briefly, while avoiding poisoning or stale authorization outcomes.

# Refresh-ahead

proactively refresh hot keys whose expiry would cause an expensive miss.

# Bounded fallback

Prevent every request from independently hitting the source during a cache failure.

# HTTP Cache

For shared HTTP caches, define Cache-Control, validators such as ETag, and variation behavior correctly. A GET request is not automatically safe to cache, and cache directives must align with the response's authorization semantics.