On Wed, Jul 22, 2015 at 10:44 AM, Robert Haas <robertmh...@gmail.com> wrote: > One thing I noticed that is a bit dismaying is that we don't get a lot > of benefit from having more workers. Look at the 0.1 data. At 2 > workers, if we scaled perfectly, we would be 3x faster (since the > master can do work too), but we are actually 2.4x faster. Each > process is on the average 80% efficient. That's respectable. At 4 > workers, we would be 5x faster with perfect scaling; here we are 3.5x > faster. So the third and fourth worker were about 50% efficient. > Hmm, not as good. But then going up to 8 workers bought us basically > nothing.
...sorry for bumping up this mail from July... I don't think you meant to imply it, but why should we be able to scale perfectly? Even when the table fits entirely in shared_buffers, I would expect memory bandwidth to become the bottleneck before a large number of workers are added. Context switching might also be problematic. I have almost no sense of whether this is below or above par, which is what I'm really curious about. FWIW, I think that parallel sort will scale somewhat better. -- Peter Geoghegan -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers