Re: walsender bug: stuck during shutdown

On 2020/11/24 5:52, Alvaro Herrera wrote:
> Hello
>
> Chloe Dives reported that sometimes a walsender would become stuck
> during shutdown and *not* shutdown, thus preventing postmaster from
> completing the shutdown cycle. This has been observed to cause the
> servers to remain in such state for several hours.
>
> After a lengthy investigation and thanks to a handy reproducer by Chris
> Wilson, we found that the problem is that WalSndDone wants to avoid
> shutting down until everything has been sent and acknowledged; but this
> test is coded in a way that ignores the possibility that we have never
> received anything from the other end. In that case, both
> MyWalSnd->flush and MyWalSnd->write are InvalidRecPtr, so the condition
> in WalSndDone to terminate the loop is never fulfilled. So the
> walsender is looping forever and never terminates, blocking shutdown of
> the whole instance.
>
> The attached patch fixes the problem by testing for the problematic
> condition.
>
> Apparently this problem has existed forever. Fujii-san almost patched
> for it in 5c6d9fc4b2b8 (2014!), but missed it by a zillionth of an inch.

Thanks for working on this!
Could you tell me the discussion thread where Chloe Dives reported the issue to?
Sorry I could not find that..
I'd like to see the procedure to reproduce the issue.

Regards,

--
Fujii Masao
Advanced Computing Technology Center
Research and Development Headquarters
NTT DATA CORPORATION