Re: ctidscan as an example of custom-scan (Re: [v9.5] Custom Plan API)

On Wed, Jul 15, 2015 at 10:12 AM, Kouhei Kaigai <kaigai(at)ak(dot)jp(dot)nec(dot)com> wrote:
> We never guarantee the interface compatibility between major version up.
> If we add/modify interface on v9.6, it is duty for developer of extensions
> to follow the new version, even not specific to custom-scan provider.
> If v9.6 adds support fine-grained function cost estimation, I also have
> to follow the feature, but it is natural.

Maintaining compatibility across major versions is a best-effort and
even if we sometimes break things across major versions, and sometimes
even silently (take the example of 9.3's background worker that do not
start with 9.4 as long as bgw_notify_pid is not set to 0), the
approach is usually taken to have APIs stable and convenient able to
cover a maximum set of cases for a given set of plugins, and this
serves well in the long term. Now it is true that we cannot assume
either that the version of a plugin API will be perfect forever and
will be able to cover all the imagined test cases at first shot, still
I'd like to think that things are broken only when necessary and with
good reasons. A set of APIs changed at each major release tends to be
proof that research lacked in the first version, and would surely
demotivate its adoption by extension developers.
--
Michael