Re: [HACKERS] background sessions

On Sat, Mar 11, 2017 at 10:11 AM, Pavel Stehule <pavel.stehule@gmail.com> wrote:
> 2017-03-09 14:52 GMT+01:00 Peter Eisentraut
> <peter.eisentraut@2ndquadrant.com>:
>>
>> On 3/8/17 14:22, Pavel Stehule wrote:
>> > 1. will be background session process closed automatically when parent
>> > process is closed?
>>
>> If the communications queue goes away the process will eventually die.
>> This is similar to how a backend process will eventually die if the
>> client goes away.  Some more testing would be good here.
>
>
> what means "eventually die"?
>
> I called pg_sleep() in called subprocess.
>
> Cancel, terminating parent process has not any effect. It is maybe
> artificial test.
>
> Little bit more realistic - waiting on table lock in background worker was
> successful - and when parent was cancelled, then worker process was
> destroyed too.
>
> But when parent was terminated, then background worker process continued.
>
> What is worse - the background worker had 100% CPU and I had to restart
> notebook.
>
> CREATE OR REPLACE FUNCTION public.foo()
>  RETURNS void
>  LANGUAGE plpythonu
> AS $function$
> with plpy.BackgroundSession() as a:
>   a.execute('update foo2 set a = 30')
>   a.execute('insert into foo2 values(10)')
> $function$
> postgres=#
>
>
> I blocked foo2 in another session.

I'm not sure what's going on with this patch set, but in general a
background process can't just go away when the foreground process goes
away.  We could arrange to kill it, a la pg_terminate_backend(), or we
can let it keep running, and either of those things might be what
somebody wants, depending on the situation.  But it can't just vanish
into thin air.

--
Robert Haas
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