Amit Langote <amitlangot...@gmail.com> writes:
> On Wed, Mar 31, 2021 at 11:56 AM Tom Lane <t...@sss.pgh.pa.us> wrote:
>> ... I've complained before that apply_scanjoin_target_to_paths
>> is brute-force and needs to be rewritten, but I don't really want to
>> undertake that task right now.
> I remember having *unsuccessfully* tried to make
> apply_scanjoin_target_to_paths() do the targetlist pushdown for the
> traditional inheritance cases as well. I agree that rethinking the
> whole apply_scanjoin_target_to_paths() approach might be a better use
> of our time. It has a looping-over-the-whole-partition-array
> bottleneck for simple lookup queries that I have long wanted to
> propose doing something about.
I was wondering if we could get anywhere by pushing more smarts
down to the level of create_projection_path itself, ie if we see
we're trying to apply a projection to an AppendPath then push it
underneath that automatically. Then maybe some of the hackery
in apply_scanjoin_target_to_paths could go away.
There's already an attempt at that in apply_projection_to_path,
but it's not completely clean so there are callers that can't
use it. Maybe a little more thought about how to do that
in a way that violates no invariants would yield dividends.
regards, tom lane
