Re: let's make the list of reportable GUCs configurable (was Re: Add%r substitution for psql prompts to show recovery status) - Mailing list pgsql-hackers

From Craig Ringer
Subject Re: let's make the list of reportable GUCs configurable (was Re: Add%r substitution for psql prompts to show recovery status)
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Msg-id CAMsr+YEEFXz_QPiGu-FND+sXJ6Mmi80i4Q43CNVNH2UQf+8-Uw@mail.gmail.com
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In response to Re: let's make the list of reportable GUCs configurable (was Re: Add %r substitution for psql prompts to show recovery status)  (Tom Lane <tgl@sss.pgh.pa.us>)
Responses Re: let's make the list of reportable GUCs configurable (was Re: Add%r substitution for psql prompts to show recovery status)
List pgsql-hackers
On 11 January 2018 at 09:55, Tom Lane <tgl@sss.pgh.pa.us> wrote:
Robert Haas <robertmhaas@gmail.com> writes:
> But if we add this feature and somebody wants to use it for
> server_version_num, it's really pretty simple.  In the startup packet,
> you say _pq_.report=server_version_num.  Then, you call
> PQparameterStatus(conn, "server_version_num").  If you don't get a
> value, you try calling PQparameterStatus(conn, "server_version") and
> extracting the second word.  If that still doesn't work then you give
> up.  That doesn't seem either useless or difficult to implement
> correctly from here.

Yeah, but what's the point?  If yuou have to maintain the server_version
parsing code anyway, you're not saving any complexity with this.  You're
just creating a code backwater that you probably won't test adequately.


If we'd done server_version_num in 9.5, for example, less stuff would've broken with pg10.

I just don't get it. The argument you use can be applied to almost any change, to say "why bother making change <x> because people can't rely on it for <y> years, so it's pointless to have it at all". Why add protocol v3?

PostgreSQL is a stable, long term project, and I'd like to plan for the future. I also think people are way more likely to handle things like --with-extra-version correctly when dealing with server_version_num, where I don't much *care* if code parsing old server versions breaks. 

--
 Craig Ringer                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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