Re: support for MERGE

From: Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
To: Pg Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: support for MERGE
Date: 2021-11-12 17:57:57
Message-ID: 202111121757.lste2omukt6p@alvherre.pgsql
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Here's a new version. Many of the old complaints have been fixed;
particularly, the handling of partitioned tables is now much cleaner and
straightforward. Amit Langote helped considerably in getting this part
to shape -- thanks for that. Amit also helped correct the EvalPlanQual
behavior, which wasn't quite up to snuff.

There are a few things that can still be improved here. For one, I need
to clean up the interactions with table AM (and thus heapam.c etc).
Secondarily, and I'm now not sure that I really want to do it, is change
the representation for executor: instead of creating a fake join between
target and source, perhaps we should have just source, and give
optimizer a separate query to fetch tuples from target.

What I did do is change how the target table is represented from parse
analysis to executor. For example, in the original code, there were two
RTEs that represented the target table; that is gone. Now the target
table is always just the query's resultRelation. This removes a good
number of ugly hacks that had been objected to.

I'll park this in the January commitfest now.

Álvaro Herrera Valdivia, Chile —
"Cómo ponemos nuestros dedos en la arcilla del otro. Eso es la amistad; jugar
al alfarero y ver qué formas se pueden sacar del otro" (C. Halloway en
La Feria de las Tinieblas, R. Bradbury)

Attachment Content-Type Size
merge-v3.patch text/x-diff 384.7 KB

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