On Fri, Mar 31, 2017 at 5:43 AM, Neha Khatri <nehakhat...@gmail.com> wrote: > > On Fri, Mar 31, 2017 at 8:29 AM, Kuntal Ghosh <kuntalghosh.2...@gmail.com> > wrote: >> >> On Fri, Mar 31, 2017 at 2:05 AM, Kuntal Ghosh >> <kuntalghosh.2...@gmail.com> wrote: >> > >> > 1. Put an Assert(0) in ParallelQueryMain(), start server and execute >> > any parallel query. >> > In LaunchParallelWorkers, you can see >> > nworkers = n nworkers_launched = n (n>0) >> > But, all the workers will crash because of the assert statement. >> > 2. the server restarts automatically, initialize >> > BackgroundWorkerData->parallel_register_count and >> > BackgroundWorkerData->parallel_terminate_count in the shared memory. >> > After that, it calls ForgetBackgroundWorker and it increments >> > parallel_terminate_count. In LaunchParallelWorkers, we have the >> > following condition: >> > if ((BackgroundWorkerData->parallel_register_count - >> > BackgroundWorkerData->parallel_terminate_count) >= >> > max_parallel_workers) >> > DO NOT launch any parallel worker. >> > Hence, nworkers = n nworkers_launched = 0. >> parallel_register_count and parallel_terminate_count, both are >> unsigned integer. So, whenever the difference is negative, it'll be a >> well-defined unsigned integer and certainly much larger than >> max_parallel_workers. Hence, no workers will be launched. I've >> attached a patch to fix this. > > > The current explanation of active number of parallel workers is: > > * The active > * number of parallel workers is the number of registered workers minus the > * terminated ones. > > In the situations like you mentioned above, this formula can give negative > number for active parallel workers. However a negative number for active > parallel workers does not make any sense. Agreed.
> I feel it would be better to explain in code that in what situations, the > formula > can generate a negative result and what that means. I think that we need to find a fix so that it never generates a negative result. The last patch submitted by me generates a negative value correctly. But, surely that's not enough. -- Thanks & Regards, Kuntal Ghosh EnterpriseDB: http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers