S3
Simple Storage Service
Amazon S3 has a simple web services interface that you can use to store and retrieve any amount of data, at any time, from anywhere on the web.
レアケースでS3が不整合になるという問題を、コストや性能を犠牲にせず解決した話（S3側のキャッシュに課題があった）
consistency witness
Witnesses are popular in distributed systems because they often only need to track a little bit of state, in-memory, without needing to go to disk. This allows them to achieve extremely high request processing rates with very low latency.
There are countless interleavings of operations and intermediate states, and at our scale, even if something happens only once in a billion requests, that means it happens multiple times per day within S3.
Common testing techniques like unit testing and integration testing are valuable, necessary tools in any production system. But they aren’t enough]when you need to build a system with such a high bar for correctness. We want a system that’s “provably correct”, not just “probably correct.” So, for strong consistency, we utilized a variety of techniques for ensuring that what we built is correct, and continues to be correct as the system evolves. We employed integration tests, deductive proofs of our proposed cache coherence algorithm, model checking to formalize our consistency design and to demonstrate its correctness, and we expanded on our model checking to examine actual runnable code.
形式手法を使って証明して、コードの検証までできるようにした？ 削除
You can delete an empty Amazon S3 bucket
AWS cliで消す
Intellijent-Tiering