Re: [HACKERS] PATCH: Keep one postmaster monitoring pipe per process

On Sat, Jul 14, 2018 at 5:34 AM, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
> On 18/04/18 09:55, Thomas Munro wrote:
>> Here's a draft patch that does that. One contentious question is:
>> should you have to opt *in* to auto-exit-on-postmaster death? Andres
>> opined that you should. I actually think it's not so bad if you don't
>> have to do that, and instead have to opt out. I think of it as a kind
>> of 'process cancellation point' or a quiet PANIC that you can opt out
>> of. It's nice to remove the old boilerplate code without having to
>> add a new boilerplate event that you have to remember every time. Any
>> other opinions?
>
> Hmm. Exiting on postmaster death by default does feel a bit too magical to
> me. But as your patch points out, there are currently no places where you
> *don't* want to exit on postmaster death, some callers just prefer to handle
> it themselves. And I like having a default or something to make sure that
> all call sites in the future will also exit quickly.
>
> I'd suggest that we add a new WL_EXIT_ON_POSTMASTER_DEATH flag, making it
> opt-on.

Ok, it's now 2 against 1. So here's a version that uses an explicit
WL_EXIT_ON_PM_DEATH value. I like that name because it's shorter and
more visually distinctive (harder to confuse with
WL_POSTMASTER_DEATH).

> But add an assertion in WaitLatchOrSocket:
>
> Assert ((wakeEvents & (WL_EXIT_POSTMASTER_DEATH | WL_POSTMASTER_DEATH)) !=
> 0);

Ok. Done for the WaitLatchXXX() interface. The WaitEventSet
interface (rarely used directly) is less amenable to that change.

Here are some of the places I had to add WL_EXIT_ON_PM_DEATH:
gather_readnext(), shm_mq_send_bytes(), shm_mq_receive_bytes(),
shm_mq_wait_internal(), ProcSleep(), ProcWaitForSignal(), pg_sleep(),
pgfdw_get_result().

Was it intentional that any of those places don't currently exit on
postmaster vaporisation?

--
Thomas Munro
http://www.enterprisedb.com