Dive deep into Cloudflare's innovative global cache purge system that operates in under 150ms. Explore the evolution from a core-based lazy purge to a coreless active purge, examining CDN basics, TTL freshness, and various purge mechanisms. Analyze the limitations of the old system and discover how the new active purge leverages RockDB for local CDN cache maintenance and a peer-to-peer data center distributed system. Compare LSM and BTree data structures, discuss performance issues, and gain insights into the inner workings of the active purge system. Conclude with a comprehensive summary and expert thoughts on this cutting-edge technology that has dramatically reduced purge times from 1.5 seconds to just 150ms.