Re: Back-patch use of unnamed POSIX semaphores for Linux?

Hi,

On 2016-12-06 21:53:06 -0500, Tom Lane wrote:
> Just saw another report of what's probably systemd killing off Postgres'
> SysV semaphores, as we've discussed previously at, eg,
> https://www.postgresql.org/message-id/flat/57828C31.5060409%40gmail.com
> Since the systemd people are generally impervious to suggestions that
> they might be mistaken, I do not expect this problem to go away.

Would doing so actually solve the systemd issue? Doesn't systemd also
remove SYSV shared memory, which we still use a tiny bit of?

> I think we should give serious consideration to back-patching commit
> ecb0d20a9, which changed the default semaphore type to unnamed-POSIX
> on Linux. We've seen no problems in the buildfarm in the two months
> that that's been in HEAD. If we don't do this, we can expect to
> continue seeing complaints of this sort until pre-v10 PG releases
> fall out of use ... and I don't want to wait that long.

I'm a bit uncomfortable backpatching this change, before it has seen
production usage. Both the posix and sysv semaphore implementation has
evolved over the years, with changing performance characteristics. I
don't think it's fair to users to swap a proven solution out for
something that hasn't seen a lot of load.

Greetings,

Andres Freund