On Fri, Jul 29, 2016 at 11:26 AM, Haribabu Kommi <kommi.harib...@gmail.com> wrote: > we observed that spawning the specified number of parallel workers for > every query that satisfies for parallelism is sometimes leading to > performance drop compared to improvement during the peak system load > with other processes. Adding more processes to the system is leading > to more context switches thus it reducing the performance of other SQL > operations. >
Have you consider to tune using max_worker_processes, basically I think even if you have kept the moderate value for max_parallel_workers_per_gather, the number of processes might increase if total number allowed is much bigger. Are the total number of parallel workers more than number of CPU's/cores in the system? If yes, I think that might be one reason for seeing performance degradation. > In order to avoid this problem, how about adding some kind of system > load consideration into account before spawning the parallel workers? > Hook could be a possibility, but not sure how users are going to decide the number of parallel workers, there might be other backends as well which can consume resources. I think we might need some form of throttling w.r.t assignment of parallel workers to avoid system overload. -- With Regards, Amit Kapila. EnterpriseDB: http://www.enterprisedb.com -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
