Re: "could not reattach to shared memory" on buildfarm member dory

Noah Misch <noah(at)leadboat(dot)com> writes:
> On Mon, Apr 30, 2018 at 08:01:40PM -0400, Tom Lane wrote:
>> What seems like a plausible theory at this point is that the apparent
>> asynchronicity is due to the allocation being triggered by a different
>> thread, and the fact that our added monitoring code seems to make the
>> failure more likely can be explained by that code changing the timing.
>> But what thread could it be? It doesn't really look to me like either
>> the signal thread or the timer thread could eat 4MB. syslogger.c
>> also spawns a thread, on Windows, but AFAICS that's not being used in
>> this test configuration.

The 1-second wait doesn't seem to have changed things much, which puts
a hole in the idea that this is triggered by a thread spawned earlier
in backend process startup.

>> Maybe the reason dory is showing the problem
>> is something or other is spawning a thread we don't even know about?

> Likely some privileged daemon is creating a thread in every new process.

Yeah, I'm afraid that's the most likely theory at this point; it offers
an explanation why we're seeing this on dory and not other machines.
Although if the daemon were responding to process startup, wouldn't the
extra wait have given it time to do so? There's still something that
doesn't add up here.

>> Any other ideas?

> PostgreSQL could retry the whole process creation, analogous to
> internal_forkexec() retries.

In the absence of any clearer theory about what's causing this,
that may be our only recourse. Sure is ugly though.

regards, tom lane