Comment by orlp

We had a similar experience in Polars trying to use io_uring.

Rust isn't inherently bad at io_uring but at least Tokio currently is. I'm not the one who implemented and benchmarked it so this is second-hand information but if I recall correctly Tokio shares one buffer pool for all threads so as you scale to 100+ threads the whole thing grinds to a halt.

Migrating our I/O to a different async runtime than Tokio was rejected. So we'll wait until it's fixed in Tokio and now use regular blocking reads instead.