Quicksilver v2: evolution of a globally distributed key-value store (Part 1)

Quicksilver is a key-value store developed by Cloudflare to provide fast global replication and low-latency access, initially designed for global configuration distribution but later becoming a foundational storage system for various products. The original Quicksilver v1 had every server maintaining a full data copy, leading to inefficiencies as the business expanded. To address this, Cloudflare introduced Quicksilver v1.5, which employs a proxy-replica design allowing some servers to act as proxies with persistent caches, significantly reducing disk usage. This new setup uses multiversion concurrency control and sliding window approaches to handle asynchronous replication and consistency challenges, ensuring sequential consistency while addressing potential negative lookups with efficient solutions like Bloom filters. The system also incorporates a Network Oracle for efficient replica discovery and connection management across data centers, maintaining low request latencies despite the architectural changes.