feat: red black tree in rust (again)

[Terkwood]

An attempt at #96 -- one which did not bear fruit! 🍎

This pull request implemented the Memtable using a Red Black Tree written in Rust. 🦀

But it doesn't look like much of an improvement, now that I have dirty_memtable.flush implemented.

Memory was quite a bit higher (1.7GB vs 400MB). PUT speed was quite a bit slower (55ms vs 37ms). GET/DELETE speeds were comparable.

Seems like it makes sense to keep the elixir agent implementation, which is simpler and easier to maintain.

1000 users spamming - rust version CSV

1000 users spamming - elixir version CSV

tasks

• [x] profile memory usage and compare
• [x] flush

alternatives

For our particular load test (raw spam of PUT/GET/PUT/DELETE of individual records, not intended to be a good proxy for any particular use case), Mutex performed better than RwLock.

Other things we tried, unsuccessfully:

• Passing around a ResourceArc and invoking it from various erlang processes: this performed no better than the naive Elixir / Agent impl.
• intrusive collections in Rust: compiler didn't like our attempt to pass mutable pointers across threads 🤷

[Terkwood]

rpds-1000-users-5s-ramp-summary.csv

[Terkwood]

.

[Terkwood]

flush-rust-summary.csv