> On 21. Aug 2019, at 20:26, Jeff Janes <jeff.janes@xxxxxxxxx> wrote: > > As noted elsewhere, v12 thwarts your attempts to deliberately design the bad estimates. You can still get them, you just have to work a bit harder at it: > > CREATE FUNCTION j (bigint, bigint) returns setof bigint as $$ select generate_series($1,$2) $$ rows 1000 language sql; Yeah, that's awesome! I didn't know about this until I ran into this issue, I'll definitely be using it for future estimation problems that are difficult to fix otherwise! > I've made an extension which has a function which always returns true, but lies about how often it is expected to return true. See the attachment. With that, you can fine-tune the planner. > > CREATE EXTENSION pg_selectivities ; Very cool and useful : )! I think in most cases I'll be okay with declaring a function with a static ROWS estimate, but I'll consider your extension if I need more flexibility in the future! Thanks Felix
