From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
cc: Tomas Vondra <tomas@vondra.me>, Jelte Fennema-Nio <postgres@jeltef.nl>,
        PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: Bump soft open file limit (RLIMIT_NOFILE) to hard limit on startup
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Comments: In-reply-to Andres Freund <andres@anarazel.de>
	message dated "Tue, 11 Feb 2025 16:14:21 -0500"
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Date: Tue, 11 Feb 2025 16:18:37 -0500
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Andres Freund <andres@anarazel.de> writes:
> My suggestion would be to redefine max_files_per_process as the number of
> files we try to be able to open in backends. I.e. set_max_safe_fds() would
> first count the number of already open fds (since those will largely be
> inherited by child processes) and then check if we can open up to
> max_files_per_process files in addition. Adjusting the RLIMIT_NOFILE if
> necessary.

Seems plausible.  IIRC we also want 10 or so FDs available as "slop"
for code that doesn't go through fd.c.

> And when using something like io_uring for AIO, it'd allow to
> max_files_per_process in addition to the files requires for the io_uring
> instances.

Not following?  Surely we'd not be configuring that so early in
postmaster start?

			regards, tom lane