RE: Partial aggregates pushdown

Hi. Mr.Momjian, Mr.Lane, Mr.Haas, hackers.

I apologize for any misunderstanding regarding the context of the attached patch and
the points on which I requested a review. Could you please allow me to clarify?

In the review around early December 2023, I received the following three issues pointed out by Mr.Haas[1].
1. Transmitting state value safely between machines
2. Making the patch clearer by adding SQL keywords
3. Fixing the behavior when the HAVING clause is present

In the email sent on February 22, 2024[2], I provided an update on the progress made in addressing these issues.
Regarding issue 1, I have only provided a proposed solution in the email and have not started the programming.
Therefore, the latest patch is not in a commit-ready state. As mentioned later, we have also temporarily reverted the
changesmade to the documentation. 
Before proceeding with the programming, I would like to discuss the proposed solution with the community and seek
consensus.
If it is necessary to have source code in order to discuss, I can create a simple prototype so that I can receive your
feedback.
Would you be able to provide your opinions on it?

Regarding issue 2., I have confirmed that creating a prototype allows us to address the issue and clear the patch.
In this prototype creation, the main purpose was to verify if the patch can be cleared and significant revisions were
madeto the previous version. 
Therefore, I have removed all the document differences.
I have submitted a patch [3] that includes the fixes for issue 3. to the patch that was posted in [2].
Regarding the proposed solution for issue 1, unlike the patch posted in [3],
we have a policy of not performing partial aggregation pushdown if we cannot guarantee compatibility and safety.
The latest patch in [3] is a POC patch. The patch that Mr. Momjian reviewed is this.
If user-facing documentation is needed for this POC patch, it can be added.

I apologize for the lack of explanation regarding this positioning, which may have caused misunderstandings regarding
thepatch posted in [3]. 

[1] https://www.postgresql.org/message-id/CA%2BTgmoYCrtOvk2f32qQKZV%3DjNL35tandf2A2Dp_2F5ASuiG1BA%40mail.gmail.com
[2]
https://www.postgresql.org/message-id/TYAPR01MB5514F0CBD9CD4F84A261198195562%40TYAPR01MB5514.jpnprd01.prod.outlook.com
[3]
https://www.postgresql.org/message-id/TYAPR01MB55141D18188AC86ADCE35FCB952F2%40TYAPR01MB5514.jpnprd01.prod.outlook.com

Sincerely yours,
Yuuki Fujii

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Yuuki Fujii
Information Technology R&D Center Mitsubishi Electric Corporation