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

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?

> ... 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.

dsm_type | critters_reporting
-----------+--------------------
posix | 69
sysv | 13
windows\r | 10
(3 rows)

regards, tom lane