Re: logicalrep_worker_launch -- counting/checking the worker limits

On Fri, Aug 11, 2023 at 2:29 PM Peter Smith <smithpb2250(at)gmail(dot)com> wrote:
>
> While reviewing other threads I have been looking more closely at the
> the logicalrep_worker_launch() function. IMO the logic of that
> function seems not quite right.
>
> Here are a few things I felt are strange:
>
...
>
> 2. There is some condition for attempting the garbage-collection of workers:
>
> /*
> * If we didn't find a free slot, try to do garbage collection. The
> * reason we do this is because if some worker failed to start up and its
> * parent has crashed while waiting, the in_use state was never cleared.
> */
> if (worker == NULL || nsyncworkers >= max_sync_workers_per_subscription)
>
> The inclusion of that nsyncworkers check here has very subtle
> importance. AFAICT this means that even if we *did* find a free
> worker, we still need to do garbage collection just in case one of
> those 'in_use' tablesync worker was in error (e.g. crashed after
> marked in_use). By garbage-collecting (and then re-counting
> nsyncworkers) we might be able to launch the tablesync successfully
> instead of just returning that it has maxed out.
>
> 2a. IIUC that is all fine. The problem is that I think there should be
> exactly the same logic for the parallel apply workers here also.
>

Did you try to reproduce this condition, if not, can you please try it
once? I wonder if the leader worker crashed, won't it lead to a
restart of the server?

--
With Regards,
Amit Kapila.