Re: shared memory based stat collector (was: Sharing record typmods between backends)

On Mon, Aug 14, 2017 at 12:16 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> On Sun, Aug 13, 2017 at 9:59 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>> In principle we could keep the existing mechanism as a fallback.
>>> Whether that's worth the trouble is debatable. The current code
>>> in initdb believes that every platform has some type of DSM support
>>> (see choose_dsm_implementation). Nobody's complained about that,
>>> and it certainly works on every buildfarm animal. So for all we know,
>>> dynamic_shared_memory_type = none is broken already.
>
>> Actually, now that you mention it, I think it *is* broken already, or
>> more to the point, if you configure that value, the autovacuum
>> launcher hangs up, because of the AutovacuumWorkItem stuff that Alvaro
>> added. When I just tested it, the AV launcher somehow ended up
>> waiting for AutovacuumLock and I had to SIGQUIT the server to shut it
>> down.
>
> Hmm, shouldn't that be an open item for v10?

I already added it.

>> ... If somebody has a system where no other form of shared
>> memory, works dynamic_shared_memory_type = mmap is still a thing, so
>> the use case for "none" seems very thin indeed. I'd vote for just
>> ripping it out in v11.
>
> Just FYI, the only values being reported by buildfarm animals are
> "posix", "sysv", and "windows". So while mmap may be a thing,
> it's an untested thing.

I'm pretty sure I dev-tested it before committing anything, but,
certainly, having ongoing BF coverage woudn't be a bad thing.

--
Robert Haas
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