On Thu, Feb 6, 2014 at 5:31 AM, Robert Haas <robertmh...@gmail.com> wrote: > Hmm, sounds a little steep. Why is it so expensive? I'm probably > missing something here, because I would have thought that planner > support for partial sorts would consist mostly of considering the same > sorts we consider today, but with the costs reduced by the batching.
I guess it's because the patch undoes some optimizations in the mergejoin planner wrt caching merge clauses and adds a whole lot of code to find_mergeclauses_for_pathkeys. In other code paths the overhead does seem to be negligible. Notice the removal of: /* Select the right mergeclauses, if we didn't already */ /* * Avoid rebuilding clause list if we already made one; * saves memory in big join trees... */ Regards, Marti -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers