Horton

Re: Unportable implementation of background worker start

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Rémi Zara <remi_zara@mac.com>
Cc: Andres Freund <andres@anarazel.de>, cm@enterprisedb.com, Alvaro Herrera <alvherre@2ndquadrant.com>, pgsql-hackers@postgresql.org
Date: 2017-04-25T15:57:30Z
Lists: pgsql-hackers 
=?utf-8?Q?R=C3=A9mi_Zara?= <remi_zara@mac.com> writes:
>> Le 25 avr. 2017 à 01:47, Tom Lane <tgl@sss.pgh.pa.us> a écrit :
>> It looks like coypu is going to need manual intervention (ie, kill -9
>> on the leftover postmaster) to get unwedged :-(.  That's particularly
>> disturbing because it implies that ServerLoop isn't iterating at all;
>> otherwise, it'd have noticed by now that the buildfarm script deleted
>> its data directory out from under it.

> coypu was not stuck (no buildfarm related process running), but failed to clean-up shared memory and semaphores.
> I’ve done the clean-up.

Huh, that's even more interesting.

Looking at the code, what ServerLoop actually does when it notices that
the postmaster.pid file has been removed is

				kill(MyProcPid, SIGQUIT);

So if our hypothesis is that pselect() failed to unblock signals,
then failure to quit is easily explained: the postmaster never
received/acted on its own signal.  But that should have left you
with a running postmaster holding the shared memory and semaphores.
Seems like if it is gone but it failed to remove those, somebody must've
kill -9'd it ... but who?  I see nothing in the buildfarm script that
would.

			regards, tom lane

Commits

  1. Cope with glibc too old to have epoll_create1().

  2. Make latch.c more paranoid about child-process cases.

  3. Allow multiple bgworkers to be launched per postmaster iteration.

  4. Revert "Use pselect(2) not select(2), if available, to wait in postmaster's loop."

  5. Use pselect(2) not select(2), if available, to wait in postmaster's loop.

  6. Run the postmaster's signal handlers without SA_RESTART.

  7. Fix postmaster's handling of fork failure for a bgworker process.

  8. Partially revert commit 536d47bd9d5fce8d91929bee3128fa1d08dbcc57.

  9. Avoid depending on non-POSIX behavior of fcntl(2).

  10. Remove long-obsolete catering for platforms without F_SETFD/FD_CLOEXEC.