Feedback-ID: ia2694551:Fastmail
Date: Fri, 13 Dec 2024 12:04:33 +0100
From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: =?utf-8?B?w5ZuZGVyIEthbGFjxLE=?= <onderkalaci@gmail.com>
Cc: Matheus Alcantara <matheusssilv97@gmail.com>, 
	Pg Hackers <pgsql-hackers@postgresql.org>
Subject: Re: Allow FDW extensions to support MERGE command via CustomScan
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On 2024-Dec-13, Önder Kalacı wrote:

> Matheus Alcantara <matheusssilv97@gmail.com> wrote:

> > I didn't understand what is a "custom scan node" on the fdw context at
> > first place (I don't know if it is an already know word on this
> > context), but from what I've understood so far, to a fdw extension
> > support MERGE it should implements on PlanForeignModify right?
> 
> In the long term, I think that's a good plan. First, the core code in
> ExecMerge() should be aware of foreign tables, then each foreign table
> should handle Merge command planning on its own PlanForeignModify.
> That'd be great, because the execution of Merge command is pretty
> complex, and in essence Postgres would be providing the solid
> infrastructure for all foreign tables.
> 
> However, I expect that to be a non-trivial patch. Instead, the goal of
> this patch is to at least let extensions to completely override the
> planning & execution via CustomScan, not confined to Postgres' foreign
> table planning & execution.

IMO this is a bad plan.  It'll become _the_ way to run MERGE on foreign
tables, which will become a selling point for proprietary FDWs, and
nobody will be motivated to write the code to implement the long-term
plan you were describing.

In short, -1 from me.

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/