Robert Haas <robertmhaas@gmail.com> writes:
> On Thu, Aug 4, 2016 at 9:57 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> [ shrug... ] What do you claim is not machine-readable about
>> server_version?
> Surely you can't have missed the connection between the issue at hand
> and what Craig is talking about. If libpq were using the
> machine-readable version rather than PARSING A STRING, switching to a
> two-part numbering scheme wouldn't force a compatibility break.
Well, yeah, this specific case would not have broken, because we
intentionally chose to maintain backwards compatibility of the
PG_VERSION_NUM data format. But I think there's nothing much except
wishful thinking backing up the idea that starting to send
server_version_num now will prevent a bug in future. If we ever do
change our version numbering scheme again, it would quite possibly
be in a way that breaks PG_VERSION_NUM as well. A fairly obvious
potential reason to need to change something there is overflow of
the two-digit fields: clients relying on PG_VERSION_NUM would be
*more* at risk, not less so, than clients looking at a string.
In short: if we'd done it that way all along, it would've been nice.
But encouraging people to change horses now isn't really going to
make things better. What is far more likely to happen, if we were
to do that, is that people will make clients that gratuitously fail
on old server versions because they didn't bother to support or test
for the case that the server doesn't send server_version_num.
You don't really want to encourage multiple ways of identifying which
software version you're dealing with. That way madness lies.
regards, tom lane
