Pavel Stehule <pavel.steh...@gmail.com> wrote: > čt 23. 4. 2020 v 7:06 odesílatel Antonin Houska <a...@cybertec.at> napsal: > > Tom Lane <t...@sss.pgh.pa.us> wrote: > > > But it's not entirely clear to me that we know the best plan for a > > statement-level RI action with sufficient certainty to go that way. > > Is it really the case that the plan would not vary based on how > > many tuples there are to check, for example? > > I'm concerned about that too. With my patch the checks become a bit slower if > only a single row is processed. The problem seems to be that the planner is > not entirely convinced about that the number of input rows, so it can still > build a plan that expects many rows. For example (as I mentioned elsewhere in > the thread), a hash join where the hash table only contains one tuple. Or > similarly a sort node for a single input tuple. > > without statistics the planner expect about 2000 rows table , no?
I think that at some point it estimates the number of rows from the number of table pages, but I don't remember details. I wanted to say that if we constructed the plan "manually", we'd need at least two substantially different variants: one to check many rows and the other to check a single row. -- Antonin Houska Web: https://www.cybertec-postgresql.com
