Re: AIO v2.5

Hi,

Attached v2.11, with the following changes:

- Pushed the smgr interrupt change, as discussed on the dedicated thread

- Pushed "bufmgr: Improve stats when a buffer is read in concurrently"

It was reviewed by Melanie and there didn't seem to be any reason to wait
further.

- Addressed feedback from Melanie

- Addressed feedback from Noah

- Added a new commit: aio: Change prefix of PgAioResultStatus values to PGAIO_RS_

As suggested/requested by Melanie. I think she's unfortunately right.

- Added a patch for some comment fixups for code that's either older or
already pushed

- Added an error check for FileStartReadV() failing

FileStartReadV() actually can fail, if the file can't be re-opened. I
thought it'd be important for the error message to differ from the one
that's issued for read actually failing, so I went with:

"could not start reading blocks %u..%u in file \"%s\": %m"

but I'm not sure how good that is.

- Added a new commit to redefine set_max_safe_fds() to not subtract
already_open fds from max_files_per_process

This prevents io_method=io_uring from failing when RLIMIT_NOFILE is high
enough, but more than max_files_per_process io_uring instances need to be
created.

- Improved error message if io_uring_queue_init() fails

Added errhint()s for likely cases of failure.

Added errcode(). I was tempted to use errcode_for_file_access(), but that
doesn't support ENOSYS - perhaps I should add that instead?

- Disable io_uring method when using EXEC_BACKEND, they're not compatible

I chose to do this with a define aio.h, but I guess we could also do it at
configure time? That seems more complicated though - how would we even know
that EXEC_BACKEND is used on non-windows?

Not sure yet how to best disable testing io_uring in this case. We can't
just query EXEC_BACKEND from pg_config.h unfortunately. I guess making the
initdb not fail and checking the error log would work, but that doesn't work
nicely with Cluster.pm.

- Changed test_aio injection short-read injection point to zero out the rest
of the IO, otherwise some tests fail to fail even if a bug in retries of
partial reads is introduced

- Improved method_io_uring.c includes a bit (no pgstat.h)

Questions:

- We only "look" at BM_IO_ERROR for writes, isn't that somewhat weird?

See AbortBufferIO(Buffer buffer)

It doesn't really matter for the patchset, but it just strikes me as an oddity.

Greetings,

Andres Freund