Designing systems to achieve perfection in consistency, availability, latency, and throughput simultaneously is a challenge. Balancing these properties is key. Bluesky made tradeoffs in design to boost performance while sacrificing some consistency, leading to a 96% reduction in P99s. With millions of users, hot shards occur when some users heavily load a shard, causing delays for others. To address this, Bluesky introduced Lossy Timelines, reducing Fanout work for users with excessive follows, improving system scalability. By embracing imperfection and using caching strategies, Bluesky saw a significant reduction in hot shards and improved Fanout time by over 90%. This approach highlights the importance of prioritizing system optimization and scalability.
https://jazco.dev/2025/02/19/imperfection/