Re: Query with high planning time at version 11.1 compared versions10.5 and 11.0

On 2018-Dec-06, Amit Langote wrote:

> The partitionwise join related
> changes in PG 11 moved the add_child_rel_equivalences call in
> set_append_rel_size such that child EC members would be added even before
> checking if the child rel is dummy, but for a reason named in the comment
> above the call:
>
>    ... Even if this child is
>  * deemed dummy, it may fall on nullable side in a child-join, which
>  * in turn may participate in a MergeAppend, where we will need the
>  * EquivalenceClass data structures.
>
> However, I think we can skip adding the dummy child EC members here  and
> instead make it a responsibility of partitionwise join code in joinrels.c
> to add the needed EC members.  Attached a patch to show what I mean, which
> passes the tests and gives this planning time:

Robert, Ashutosh, any comments on this?  I'm unfamiliar with the
partitionwise join code.