Re: test_shm_mq failing on anole (was: Sending out a request for more buildfarm animals?)

On 2014-09-29 14:46:20 -0400, Robert Haas wrote:
> On Fri, May 9, 2014 at 10:18 AM, Robert Haas <robertmhaas@gmail.com> wrote:
> > On Sat, May 3, 2014 at 4:31 AM, Dave Page <dave.page@enterprisedb.com> wrote:
> >> Hamid@EDB; Can you please have someone configure anole to build git
> >> head as well as the other branches? Thanks.
> >
> > The test_shm_mq regression tests hung on this machine this morning.
> > Hamid was able to give me access to log in and troubleshoot.
> > Unfortunately, I wasn't able to completely track down the problem
> > before accidentally killing off the running cluster, but it looks like
> > test_shm_mq_pipelined() tried to start 3 background workers and the
> > postmaster only ever launched one of them, so the test just sat there
> > and waited for the other two workers to start.  At this point, I have
> > no idea what could cause the postmaster to be asleep at the switch
> > like this, but it seems clear that's what happened.
> 
> This happened again, and I investigated further.  It looks like the
> postmaster knows full well that it's supposed to start more bgworkers:
> the ones that never get started are in the postmaster's
> BackgroundWorkerList, and StartWorkerNeeded is true.  But it only
> starts the first one, not all three.  Why?

Not necessarily related, but one interesting tidbit is that fork isn't
mentioned to be async signal safe on HP-UX:
http://nixdoc.net/man-pages/HP-UX/man5/thread_safety.5.html#Async%20Signal%20Safe

I have some doubts that fork() really could be not signal safe, but it's
a bit odd. IIRC posix requires fork() to be async safe, at least if
threads aren't present.

I'm generally baffled at all the stuff postmaster does in signal
handlers... ProcessConfigFile(), load_hba() et al. It's all done with
signals disabled, but still.

Greetings,

Andres Freund

-- Andres Freund                       http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services