On Wed, Mar 16, 2016 at 2:02 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: > Robert Haas <robertmh...@gmail.com> writes: >> On Wed, Mar 16, 2016 at 12:57 PM, Tom Lane <t...@sss.pgh.pa.us> wrote: >>> Yeah, I was thinking about the same thing. The comment block above >>> where you're looking would need some adjustment. > >> OK, how about this? > > Looks pretty close. One point is that if we do end up using a Result > node, then the parent GatherPath does not get charged for the Result > node's cpu_per_tuple overhead. I'm not sure that that's worth changing > though. It's probably better to bet that the subpath is projectable and > so no cost will ensue, than to bet the other way.
I'm almost sure this way is the better bet. I actually think at present the GatherPath is always on top of a scan or join, and those all project. There might be other cases in the future that don't, but I think it'd be fine to leave off worrying about this until we (a) find a case where it happens and (b) failing to charge for the Result causes a problem. The current situation of never projecting in the workers is far worse. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
