On 08/10/15 17:09, Robert Haas wrote: > - You consider pushing down ORDER BY if any prefix of the query > pathkeys satisfy is_foreign_expr(), but that doesn't seem right to me. > If the user says SELECT * FROM remotetab ORDER BY a, unsafe(a), > ordering the result set by a doesn't help us much. We've talked a few > times about an incremental sort capability that would take a stream of > tuples already ordered by one or more columns and sort each group by > additional columns, but I don't think we have that currently. Without > that capability, I don't think there's much benefit in sorting by a > prefix of the pathkeys. I suspect that if we can't get them all, it's > not worth doing.
That depends how often the additional columns affect the sorted order, if the sort method takes advantage of sorted input. -- Jeremy -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers