Re: strange parallel query behavior after OOM crashes

    parallel_register_count - parallel_terminate_count

Can active workers ever be greater than max_parallel_workers, I think no. Then why should there be greater than check in the following condition:

I feel there should be an assert if

    (BackgroundWorkerData->parallel_register_count - BackgroundWorkerData->parallel_terminate_count) > max_parallel_workers)

And the check could be 

    if (parallel && (active_parallel_workers == max_parallel_workers))

        then do not register new parallel wokers and return.

There should be no tolerance for the case when active_parallel_workers > max_parallel_workers. After all that is the purpose of max_parallel_workers.

Is it like multiple backends trying to register parallel workers at the same time, for which the greater than check should be present?

Thoughts?