From: Tom Lane <tgl@sss.pgh.pa.us>
To: Alex Hunsaker <badalex@gmail.com>
cc: Robert Haas <robertmhaas@gmail.com>,
        "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Subject: Re: Back-patch use of unnamed POSIX semaphores for Linux?
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Comments: In-reply-to Alex Hunsaker <badalex@gmail.com>
	message dated "Wed, 07 Dec 2016 14:37:53 -0700"
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Date: Wed, 07 Dec 2016 17:42:52 -0500
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Alex Hunsaker <badalex@gmail.com> writes:
> On Wed, Dec 7, 2016 at 1:12 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> But this is all kind of moot if Peter is right that systemd will zap
>> POSIX shmem along with SysV semaphores.  I've been trying to reproduce
>> the issue on a Fedora 25 installation, and so far I can't get it to
>> zap anything, so I'm a bit at a loss how to prove things one way or
>> the other.

> After logon, you should see "/usr/lib/systemd/systemd --user" running for
> that user. After logout out, said proc should exit.

Hmm ... after further experimentation, I still can't get this version of
systemd (231) to do anything evil.  It turns out that Fedora ships it with
KillUserProcesses turned off by default, and maybe having that on is a
prerequisite for the other behavior?  But that doesn't make a lot of sense
because we'd never be seeing the reports of databases moaning about lost
semaphores if the processes got killed first.  Anyway, I see nothing bad
happening if KillUserProcesses is off, while if it's on then the database
gets shut down reasonably politely via SIGTERM.

Color me confused ... maybe systemd's behavior has changed?

			regards, tom lane


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