Re: support for MERGE

Hi,

On 2022-01-28 17:27:37 -0300, Alvaro Herrera wrote:
> MERGE, v10.  I am much more comfortable with this version; I have
> removed a bunch of temporary hacks and cleaned up the interactions with
> table AM and executor, which is something that had been bothering me for
> a while.  The complete set of changes can be seen in github,
> https://github.com/alvherre/postgres/commits/merge-15

Any chance you could split this into something more reviewable? The overall
diff stats are: 102 files changed, 8589 insertions(+), 234 deletions(-) thats
pretty hard to really review. Incremental commits don't realy help with that.


> I am not aware of anything of significance in terms of remaining work
> for this project.

One thing from skimming: There's not enough documentation about the approach
imo - it's a complicated enough feature to deserve more than the one paragraph
in src/backend/executor/README.


I'm still [1],[2] uncomfortable with execMerge.c kinda-but-not-really being an
executor node.


> The one thing I'm a bit bothered about is the fact that we expose a lot of
> executor functions previously static.  I am now wondering if it would be
> better to move the MERGE executor support functions into nodeModifyTable.c,
> which I think would mean we would not have to expose those function
> prototypes.

I'm worried about the complexity of nodeModifyTuple.c as is. Moving more code

in there does not seem like the right call to me - we should do the opposite
if anything.


A few inline comments below. No real review, just stuff noticed while skimming
to see where this is at.


Greetings,

Andres


[1] https://www.postgresql.org/message-id/20180405200003.gar3j26gsk32gqpe@alap3.anarazel.de
[2] https://www.postgresql.org/message-id/20180403021800.b5nsgiclzanobiup@alap3.anarazel.de