Re: [PATCH] Hooks at XactCommand level

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Gilles Darold <gilles(at)darold(dot)net>, Nicolas CHAHWEKILIAN <leptitstagiaire(at)gmail(dot)com>, pgsql-hackers(at)lists(dot)postgresql(dot)org
Subject: Re: [PATCH] Hooks at XactCommand level
Date: 2021-07-30 21:49:09
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Andres Freund <andres(at)anarazel(dot)de> writes:
> On 2021-07-30 13:58:51 -0400, Tom Lane wrote:
>> I've not read this version of the patch, but I see from the cfbot's
>> results that it's broken postgres_fdw.

> I think this may partially be an issue with the way that postgres_fdw
> uses the callback than with the patch. It disconnects from the server
> *regardless* of the XactEvent passed to the callback. That makes it
> really hard to extend the callback mechanism to further events...

Perhaps. Nonetheless, I thought upthread that adding these events
as Xact/SubXactCallback events was the wrong design, and I still
think that. A new hook would be a more sensible way.

> I'm *very* unconvinced it makes sense to implement a feature like this
> in an extension / that we should expose API for that purpose. To me the
> top-level transaction state is way too tied to our internals for it to
> be reasonably dealt with in an extension.

Yeah, that's the other major problem --- the use-case doesn't seem
very convincing. I'm not even sold on the goal, let alone on trying
to implement it by hooking into these particular places. I think
that'll end up being buggy and fragile as well as not very performant.

regards, tom lane

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