Buddy, you've hit the nail on the head. Everything is a trade-off. For a stream processing system, I believe it's entirely possible to balance cost, ease of use, and latency. AutoMQ(https://github.com/AutoMQ/automq) is also a stream system built on top of S3. Its storage scheme introduces a very small size of EBS storage as a persistent write cache, and then asynchronously compacts the memory data to S3, taking into account latency while retaining the advantages of warpstream. Tiered-storage is just a form, how to implement it depends on you.