On Wed, Apr 5, 2017 at 5:34 PM, Kuntal Ghosh
<kuntalghosh.2007@gmail.com> wrote:
On Tue, Apr 4, 2017 at 12:16 PM, Neha Khatri <nehakhatri5@gmail.com> wrote:
> I feel there should be an assert if
> (BackgroundWorkerData->parallel_register_count -
> BackgroundWorkerData->parallel_terminate_count) > max_parallel_workers)
>
Backend 1 > SET max_parallel_worker = 8;
Backend 1 > Execute a long running parallel query q1 with number of
parallel worker spawned is say, 4.
Backend 2> SET max_parallel_worker = 3;
Backend 2 > Execute a long running parallel query q2 with number of
parallel worker spawned > 0.
The above assert statement will bring down the server unnecessarily
while executing q2.
Right, with multiple backends trying to fiddle with max_parallel_workers, that might bring the server down with the said assert:
Assert(parallel_register_count - parallel_terminate_count <= max_parallel_workers)
The problem here seem to be the change in the max_parallel_workers value while the parallel workers are still under execution. So this poses two questions:
1. From usecase point of view, why could there be a need to tweak the max_parallel_workers exactly at the time when the parallel workers are at play.
2. Could there be a restriction on tweaking of max_parallel_workers while the parallel workers are at play? At least do not allow setting the max_parallel_workers less than the current # of active parallel workers.
