Re: Retire has_multiple_baserels()

Aleksander Alekseev <aleksander(at)timescale(dot)com> writes:
>> The function has_multiple_baserels() is used in set_subquery_pathlist()
>> to check and see if there are more than 1 base rel, by looping through
>> simple_rel_array[]. I think one simpler way to do that is to leverage
>> root->all_baserels by
>> bms_membership(root->all_baserels) == BMS_MULTIPLE

> I used the following patch to double check that nothing was missed:
> ...
> It wasn't. The patch LGTM.

I thought this test wasn't too complete, because has_multiple_baserels
isn't reached at all in many cases thanks to the way the calling if()
is coded. I tried testing like this instead:

diff --git a/src/backend/optimizer/path/allpaths.c b/src/backend/optimizer/path/allpaths.c
index eea49cca7b..3f6fc51fb4 100644
--- a/src/backend/optimizer/path/allpaths.c
+++ b/src/backend/optimizer/path/allpaths.c
@@ -2649,6 +2649,8 @@ set_subquery_pathlist(PlannerInfo *root, RelOptInfo *rel,
*/
remove_unused_subquery_outputs(subquery, rel, run_cond_attrs);

+ Assert(has_multiple_baserels(root) == (bms_membership(root->all_baserels) == BMS_MULTIPLE));
+
/*
* We can safely pass the outer tuple_fraction down to the subquery if the
* outer level has no joining, aggregation, or sorting to do. Otherwise

and came to the same conclusion: check-world finds no cases where
the assertion fails. So it LGTM too. Pushed.

regards, tom lane