Cache-invalidering — at holde cached data konsistent med kilden til sandheden — er berømt for at være et af de sværeste problemer inden for computing. Udfordringen er at sikre, at caches ikke serverer forældet data, samtidig med at man balancerer ydeevne, konsistens og kompleksitet. Flere strategier og faldgruber er værd at forstå.
Kerneproblemeet
When the source data changes, the cached copy becomes STALE.
→ Serve stale data? (fast but wrong) vs invalidate? (consistent but complex/slower)
→ "There are only two hard things in CS: cache invalidation and naming things."
The difficulty: knowing WHEN and WHAT to invalidate, across distributed systems,
without races, while keeping good cache hit rates.
