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

On Wed, Oct 21, 2020 at 3:02 PM Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.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.