David G Johnston <david.g.johns...@gmail.com> writes: > Tom Lane-2 wrote >> [ shrug... ] The estimated value is the planner's estimate of what would >> happen *if you ran the node to completion*, which in practice doesn't >> happen because of the LIMIT.
> I don't see how a sort node cannot run to completion... The sort must have read all of its *input*, or it can't be sure it's giving the correct first result row. But "run to completion" means that it delivered all of its *output*, which obviously does not happen when under a LIMIT. It's entirely possible BTW that the sort's internal processing is not complete when it starts returning rows. For example, when we do a spill-to-disk merge sort, the final merge pass is typically done on-the-fly while returning rows, and so some fraction of that processing may never be completed if the query stops early. It's still seen all the input rows, but it hasn't completely determined their ordering. regards, tom lane -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers