On Tue, Jun 21, 2016 at 11:17:19AM -0400, Robert Haas wrote: > If the index scans are parameterized by values from the seq scan, > which is likely the situation in which this sort of plan will be > generated, we'll pay the extra cost of building the hash table once > per row in something_big. > > I think we should consider switching from a nested loop to a hash join > on the fly if the outer relation turns out to be bigger than expected. > We could work out during planning what the expected breakeven point > is; if the actual outer row count passes that, switch to a hash join. > This has been discussed before, but nobody's tried to do the work, > AFAIK.
Yes, the idea of either adjusting the execution plan when counts are inaccurate, or feeding information about misestimation back to the optimizer for future queries is something I hope we try someday. -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + As you are, so once was I. As I am, so you will be. + + Ancient Roman grave inscription + -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers