> With IOPOLL, completion events are polled directly from the NVMe device queue, either by the application or by the kernel SQPOLL thread (cf. Section 2), replacing interrupt-based signaling. This removes interrupt setup and handling overhead but disables non-polled I/O, such as sockets, within the same ring.

> Treating io_uring as a drop-in replacement in a traditional I/O-worker design is inadequate. Instead, io_uring requires a ring-per-thread design that overlaps computation and I/O within the same thread.

1) So does this mean that if you want to take advantage of IOPOLL, you should use two rings per thread: one for network and one for storage?

2) SQPoll is shown in the graph as outperforming IOPoll. I assume both polling options are mutually exclusive?

3) I'd be interested in what the considerations are (if any) for using IOPoll over SQPoll.

4) Additional question: I assume for a modern DBMS you would want to run this as thread-per core?

This sounds strange to me, of not requiring fsync. I may be wrong, but if it was meant that Enterprise SSDs have buffers and power-failure safety modes which works fine without explicit fsync, I think it's too optimistic view here.

The practical guidelines are useful. Basically “first prove I/O is actually your bottleneck, then change the architecture to use async/batching, and only then reach for features like fixed buffers / zero-copy / passthrough / polling.”

I'm curious, how sensitive are the results to kernel version & deployment environments? Some folks run LTS kernels and/or containers where io_uring may be restricted by default.

Which userspace libraries support this?. Liburing does, but Zig's Standard Library (relevant because a tigerbeetler wrote the article) does not, just silently gives out corrupt values from the completion queue.

On the rust side, rustix_uring does not support this, but widely doesn't let you set kernel flags for something it doesn't support. tokio-rs/io-uring looks like it might from the docs, but I can't figure out how (if anyone uses it there, let me know).