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From: Tom Lane <[email protected]>
To: Jelte Fennema-Nio <[email protected]>
Cc: PostgreSQL-development <[email protected]>
Cc: Andres Freund <[email protected]>
Subject: Re: Bump soft open file limit (RLIMIT_NOFILE) to hard limit on startup
Date: Tue, 11 Feb 2025 15:00:22 -0500
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <CAGECzQQh6VSy3KG4pN1d=h9J=D1rStFCMR+t7yh_Kwj-g87aLQ@mail.gmail.com>
	<[email protected]>

I wrote:
> Maybe a sanity limit on how high we'll try to raise the ulimit
> would help.

Oh, I'd forgotten that we already have one: max_files_per_process.
Since that's only 1000 by default, this patch doesn't actually have
any effect (on Linux anyway) unless the DBA raises
max_files_per_process.  That alleviates my concern quite a bit.

... but not completely.  You didn't read all of Pid Eins' advice:

    If said program you hack on forks off foreign programs, make sure
    to reset the RLIMIT_NOFILE soft limit back to 1024 for them. Just
    because your program might be fine with fds >= 1024 it doesn't
    mean that those foreign programs might. And unfortunately
    RLIMIT_NOFILE is inherited down the process tree unless explicitly
    set.

I think we'd need to pay some attention to that in e.g. COPY FROM
PROGRAM.  I also wonder whether plperl, plpython, etc can be
guaranteed not to run any code that depends on select(2).

			regards, tom lane

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