Re: A new function to wait for the backend exit after termination

On Wed, Oct 21, 2020 at 6:43 PM Magnus Hagander <magnus@hagander.net> wrote:
>
> I think it would be nicer to have a pg_terminate_backend(pid, wait=false), so a function with a second parameter
whichdefaults to the current behaviour of not waiting. And it might be a good idea to also give it a timeout parameter? 
>

Done.

>
>> 2. pg_wait_backend() -- which waits for a given backend process. Note that this function has to be used carefully
afterpg_terminate_backend(), if used on a backend that's not ternmited it simply keeps waiting in a loop. 
>
> It seems this one also very much would need a timeout value.
>

Done.

>
> And surely we should show some sort of wait event when it's waiting.
>

Added two wait events.

>
>> If the backend is terminated within the user specified timeout then
>> the function returns true, otherwise false.
>
> I’m suggesting an option for the second case to fail instead of returning false.
>

Done.

>
> > I could imagine, in theory at least, wanting to wait for a backend to go idle as well as for it disappearing.
Scopecreep in terms of this patch's goal but worth at least considering now. 
>
> IIUC, do we need a new option, something like pg_wait_backend(pid,
> timeout, waituntil) where "waituntil" if specified "idle" waits until
> the given backend goes to idle mode, or "termination" waits until
> termination?
>

Done.

Attaching a v2 patch herewith.

Thoughts and feedback are welcome.

Below things are still pending, which I plan to work on soon:

1. More testing and addition of test cases into the regression test suite.
2. Addition of the new function information into the docs.


With Regards,
Bharath Rupireddy.
EnterpriseDB: http://www.enterprisedb.com