On Mon, Mar 7, 2016 at 2:13 PM, Peter Geoghegan <p...@heroku.com> wrote: > On Mon, Mar 7, 2016 at 4:04 AM, Amit Kapila <amit.kapil...@gmail.com> wrote: >> Your point is genuine, but OTOH let us say if max_parallel_degree = 1 means >> parallelism is disabled then when somebody sets max_parallel_degree = 2, >> then it looks somewhat odd to me that, it will mean that 1 worker process >> can be used for parallel query. > > I'm not sure that that has to be true. > > What is the argument for only using one worker process, say in the > case of parallel seq scan? I understand that parallel seq scan can > consume tuples itself, which seems like a good principle, but how far > does it go, and how useful is it in the general case? I'm not > suggesting that it isn't, but I'm not sure. > > How common is it for the leader process to do anything other than > coordinate and consume from worker processes?
1 worker is often a very big speedup vs. 0 workers, and the work can easily be evenly distributed between the worker and the leader. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers