This week in caching: the second hard problem

This week in caching: the second hard problem
Invalidation, the half of the famous joke nobody solves cleanly:
— TTL vs event-based vs versioned keys — a decision matrix for when to expire on a clock, on a write, or by bumping a key suffix.
— Cache-aside vs write-through vs write-behind — the consistency trade-offs of each, with the dual-write race that bites cache-aside.
— Tag-based invalidation — how surrogate keys (Fastly) and cache tags (Symfony) let you purge 'everything touching product 451' in one call.
— Why deleting beats updating on write — the lazy-fill argument against keeping cache in sync.
Credits: the AWS caching whitepaper and Symfony cache docs.
Bookmark: the cache-aside dual-write race writeup — the bug that ships to prod looking correct.