Meet Chrono, our scalable, consistent, metadata caching solution

This post introduces Chrono, a scalable, consistent metadata caching solution built on top of Dropbox's Panda key-value storage system. Chrono addresses the challenge of serving high read query volumes while maintaining read-after-write consistency, a critical requirement for internal metadata clients. It achieves this by decoupling write attempt tracking (Chrono Server) from data caching (Memcache). Chrono Server provides an `Attempt` API to notify of write attempts and a `LatestAttemptTimestamp` API to retrieve the highest observed attempt timestamp for a key. This information is used by the Memcache layer to detect and avoid serving stale data, ensuring clients receive up-to-date metadata.