> On 21. Aug 2019, at 20:26, Jeff Janes <jeff.ja...@gmail.com> 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
