Date: Wed, 3 Jul 2019 14:29:22 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: David Rowley <david.rowley@2ndquadrant.com>,
	Jesper Pedersen <jesper.pedersen@redhat.com>,
	Andres Freund <andres@anarazel.de>,
	Robert Haas <robertmhaas@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: POC: converting Lists into arrays
Message-ID: <20190703182922.GA14665@alvherre.pgsql>
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On 2019-Jul-03, Tom Lane wrote:

> David Rowley <david.rowley@2ndquadrant.com> writes:
> > 10. I wonder if we can reduce a bit of pain for extension authors by
> > back patching a macro that wraps up a lnext() call adding a dummy
> > argument for the List.
> 
> I was wondering about a variant of that yesterday; specifically,
> I thought of naming the new 2-argument function list_next() not lnext().
> Then we could add "#define list_next(l,c) lnext(c)" in the back branches.
> This would simplify back-patching code that used the new definition, and
> it might save some effort for extension authors who are trying to maintain
> cross-branch code.  On the other hand, it's more keystrokes forevermore,
> and I'm not entirely convinced that code that's using lnext() isn't likely
> to need other adjustments anyway.  So I didn't pull the trigger on that,
> but if people like the idea I'd be okay with doing it like that.

I was thinking about this issue too earlier today, and my conclusion is
that the way you have it in v7 is fine, because lnext() callsites are
not that numerous, so the cost to third-party code authors is not that
high; the other arguments trump this consideration IMO.  I say this as
someone who curses every time he has to backpatch things across the
heap_open / table_open change -- but there are a lot more calls of that.

> Indeed.  I don't want to expend a lot of effort keeping it in sync
> with master over a long period, either.  Opinions?

Yeah, let's get it done soon.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services