From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: pgsql-hackers@postgresql.org <pgsql-hackers@postgresql.org>
Subject: Re: Back-patch use of unnamed POSIX semaphores for Linux?
Date: Tue, 06 Dec 2016 23:54:43 -0500
Message-ID: <4886.1481086483@sss.pgh.pa.us> (raw)
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References: <32387.1481079186@sss.pgh.pa.us>
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Robert Haas <robertmhaas@gmail.com> writes:
> On Tue, Dec 6, 2016 at 9:53 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> I think we should give serious consideration to back-patching commit
>> ecb0d20a9, which changed the default semaphore type to unnamed-POSIX
>> on Linux.
> Urk. That sounds like a scary thing to back-patch.
I don't deny that it's scary, but the alternative seems to be to be
rather badly broken on systemd-using distros for years to come.
That's pretty scary too.
> ... Granted, that might not
> happen, because maybe unnamed POSIX semas are one of those really
> awesome operating system primitives that never has problems on any
> system anywhere ever. But I think it's pretty hard to be certain of
> that.
You're attacking a straw man. I didn't propose changing our behavior
anywhere but Linux. AFAIK, on that platform unnamed POSIX semaphores
are futexes, which have been a stable feature since 2003 according to
https://en.wikipedia.org/wiki/Futex#History. Anybody who did need
to compile PG for use with a pre-2.6 kernel could override the default,
anyway.
Now, I did think of a problem we'd have to deal with, which is how
to avoid breaking ABI by changing sizeof(PGSemaphoreData). I think
that's soluble though.
regards, tom lane
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To: pgsql-hackers@postgresql.org
Cc: tgl@sss.pgh.pa.us, robertmhaas@gmail.com
Subject: Re: Back-patch use of unnamed POSIX semaphores for Linux?
In-Reply-To: <4886.1481086483@sss.pgh.pa.us>
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