postgresql.conf.sample ordering for IO, worker related GUCs

Hi,

While working on polishing the AIO patchset, I was trying to figure out where
to fit the new GUCs. So far I had a new "top-level" #--- style section named
"WIP AIO GUC docs" which I suspect you all won't let me get away with.

There is an existing (sub-)section which already has a few related GUCs and
could fit AIO related ones.

#------------------------------------------------------------------------------
# RESOURCE USAGE (except WAL)
#------------------------------------------------------------------------------
...
# - Asynchronous Behavior -

Except that the list of GUCs in it seems confusing:

#backend_flush_after = 0 # measured in pages, 0 disables
#effective_io_concurrency = 1 # 1-1000; 0 disables prefetching
#maintenance_io_concurrency = 10 # 1-1000; 0 disables prefetching
#io_combine_limit = 128kB # usually 1-32 blocks (depends on OS)
#max_worker_processes = 8 # (change requires restart)
#max_parallel_workers_per_gather = 2 # limited by max_parallel_workers
#max_parallel_maintenance_workers = 2 # limited by max_parallel_workers
#max_parallel_workers = 8 # number of max_worker_processes that
# can be used in parallel operations
#parallel_leader_participation = on

The first four GUCs make some sense under the heading, but why are the worker
GUCs in the same section?

Seems like it would make sense to introduce a new "Worker Processes"
sub-section?

I am wondering if it'd be better to get rid of "Asynchronous Behavior" and
instead have "# - IO -" or such? E.g. io_combine_limit isn't really about
anything asynchronous, but still seems like it should belong in the same
section as the rest?

I also wonder if fsync, recovery_init_sync_method, data_sync_retry shouldn't
be in that new subsection. Or maybe it should even be a top-level section.

FWIW, AIO currently adds the following GUCs:

#io_method = worker # worker, io_uring, sync
# (change requires restart)
#io_max_concurrency = -1 # Max number of IOs that may be in
# flight at the same time in one backend
# (change requires restart)
#io_workers = 3 # 1-32; relevant only if io_method = worker

Greetings,

Andres Freund