Re: Backends stunk in wait event IPC/MessageQueueInternal

On Fri, 13 May 2022 at 22:08, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Fri, May 13, 2022 at 6:16 AM Japin Li <japinli(at)hotmail(dot)com> wrote:
>> The process cannot be terminated by pg_terminate_backend(), although
>> it returns true.
>
> pg_terminate_backend() just sends SIGINT. What I'm wondering is what
> happens when the stuck process receives SIGINT. It would be useful, I
> think, to check the value of the global variable InterruptHoldoffCount
> in the stuck process by attaching to it with gdb. I would also try
> running "strace -p $PID" on the stuck process and then try terminating
> it again with pg_terminate_backend(). Either the system call in which
> it's currently stuck returns and then it makes the same system call
> again and hangs again ... or the signal doesn't dislodge it from the
> system call in which it's stuck in the first place. It would be useful
> to know which of those two things is happening.
>
> One thing I find a bit curious is that the top of the stack in your
> case is ioctl(). And there are no calls to ioctl() anywhere in
> latch.c, nor have there ever been. What operating system is this? We
> have 4 different versions of WaitEventSetWaitBlock() that call
> epoll_wait(), kevent(), poll(), and WaitForMultipleObjects()
> respectively. I wonder which of those we're using, and whether one of
> those calls is showing up as ioctl() in the stacktrace, or whether
> there's some other function being called in here that is somehow
> resulting in ioctl() getting called.

Thanks for your advice. I will try this on Monday.

--
Regrads,
Japin Li.
ChengDu WenWu Information Technology Co.,Ltd.