It seems very much like the B+ tree approach is just a mental model put on top of the exact same idea that is being argued against. The initial list of "bad things about LSM approaches" has almost exactly the same items on it as the list of features the B+ approach claims to achieve.

Maybe I'm getting this all wrong, but aren't the leaves also representing chunked data, which is compressed.

The Prometheus solution also sequentially places compressed chunks for the same series. The time slicing actually has a lot of benefits and can simply be seen as the first level of the described B+ tree. An index of chunks for a series can then be seen as the second level.

The potential read amplification here seems completely equivalent. Just from my high-level view, all properties of the read and write path seem almost identical.

> I don't believe this will work out well because it will introduce read amplification during query time (compared to file per series approach that they're using now).

It'll end up about the same in practice, only the time series data that needs to be read is read.

Query performance is looking quite a bit better with this design.

> And I'm really curious how they managed to get 20M writes per second on laptop.

I understand that was a micro-benchmark of one part of the system. The whole system is looking to be roughly in line with the Gorilla numbers.