What is Cache Consistency?

What is Cache Consistency?

• A. The property that cache entries always reflect the latest database state.
• B. The challenge that arises because most systems write to the database first but read from the cache, creating a window of stale data.
• C. A pattern where the cache automatically evicts on write.
• D. A technique to pre-warm the cache.

Answer: (B)

Cache consistency is about ensuring that reads reflect the latest updates across the cache and the underlying data store. When a system writes to the database but serves reads from the cache, there can be a window where the cache still holds the old value. During that window, a read may return stale data, which is the core challenge of cache consistency. The described scenario captures this mismatch between the write path and the read path, producing potential stale results. The other ideas describe idealized behavior or different cache mechanics (like eviction on write or pre-warming) that don’t address the correctness issue of keeping cached data in sync with the database.

Cache consistency is about ensuring that reads reflect the latest updates across the cache and the underlying data store. When a system writes to the database but serves reads from the cache, there can be a window where the cache still holds the old value. During that window, a read may return stale data, which is the core challenge of cache consistency. The described scenario captures this mismatch between the write path and the read path, producing potential stale results. The other ideas describe idealized behavior or different cache mechanics (like eviction on write or pre-warming) that don’t address the correctness issue of keeping cached data in sync with the database.