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

On Wed, Oct 21, 2020 at 3:02 PM Bharath Rupireddy <
bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:

> Hi,
>
> Currently pg_terminate_backend(), sends SIGTERM to the backend process but
> doesn't ensure it's exit. There are chances that backends still are
> running(even after pg_terminate_backend() is called) until the interrupts
> are processed(using ProcessInterrupts()). This could cause problems
> especially in testing, for instance in a sql file right after
> pg_terminate_backend(), if any test case depends on the backend's
> non-existence[1], but the backend is not terminated. As discussed in [1],
> we have wait_pid()(see regress.c and sql/dblink.sql), but it's not usable
> across the system. In [1], we thought it would be better to have functions
> ensuring the backend's exit on the similar lines of pg_terminate_backend().
>
> I propose to have two functions:
>
> 1. pg_terminate_backend_and_wait() -- which sends SIGTERM to the backend
> and wait's until it's exit.
>

I think it would be nicer to have a pg_terminate_backend(pid, wait=false),
so a function with a second parameter which defaults to the current
behaviour of not waiting. And it might be a good idea to also give it a
timeout parameter?

> 2. pg_wait_backend() -- which waits for a given backend process. Note that
> this function has to be used carefully after pg_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.

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

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