On 14 March 2016 at 14:52, James Sewell <james.sew...@lisasoft.com> wrote: > One question - how is the upper limit of workers chosen?
See create_parallel_paths() in allpaths.c. Basically the bigger the relation (in pages) the more workers will be allocated, up until max_parallel_degree. There is also a comment in that function which states: /* * Limit the degree of parallelism logarithmically based on the size of the * relation. This probably needs to be a good deal more sophisticated, but we * need something here for now. */ So this will likely see some revision at some point, after 9.6. -- David Rowley http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers