Re: v10 pg_ctl compatibility

On Tue, Sep 26, 2017 at 12:29 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:

> Hi,
>
> On 2017-09-26 11:59:42 -0700, Jeff Janes wrote:
> > Should the release notes have a compatibility entry about pg_ctl restart,
> > being used against a running pre-10 server, no longer being able to
> detect
> > when startup is complete?
> >
> > I don't know if cross-version use of pg_ctl restart was ever officially
> > supported, but the current behavior is rather confusing (waiting for a
> long
> > time, and then reporting failure, even though it started successfully).
>
> I'm actually tempted to just make pg_ctl verify the right version of
> postgres is being used. Maybe I'm missing something, but what's the
> use-case for allowing it, and every couple releases have some breakage?
>

The use case for me is that I have multiple versions of postgres running on
the same machine, and don't want check which pg_ctl is in my path each time
I change one of their configurations and need to restart it. Or at least,
I never had to check before, as pg_ctl goes out of its way to restart it
with the same bin/postgres that the server is currently running with,
rather than restarting with the bin/postgres currently in the path, or
whichever bin/postgres is in the same directory as the bin/pg_ctl. (Which
is itself not an unmitigated win, but it is what I'm used to).

Admittedly, this is a much bigger problem with hacking/testing than it is
with production use, but still I do have production machines with mixed
versions running, and can see myself screwing this up a few times once one
of them gets upgraded to v10, even with an incompatibility warning in the
release notes. But at least I had fair warning.

To add insult to injury, when v10 pg_ctl does restart a pre-10 server and
it sits there for a long time waiting for it to start up even though it has
already started up, if I hit ctrl-C because I assume something is horribly
wrong, it then goes ahead and kills the successfully started-and-running
server.

If we do want to do a version check and fail out, I think it should check
before shutting it down, rather than shutting it down and then refusing to
start.

Cheers,

Jeff