Re: pg_waldump stucks with options --follow or -f and --stats or -z

On Thu, Nov 18, 2021 at 12:05 AM Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:
>
> On 2021-Nov-17, Bharath Rupireddy wrote:
>
> > On Wed, Nov 17, 2021 at 7:49 AM Michael Paquier <michael(at)paquier(dot)xyz> wrote:
> > >
> > > At the same time, we could also just let things as they are. --follow
> > > and --stats being specified together is what the user looked for, so
> > > they get what they wanted.
> >
> > I think the existing way of pg_waldump getting stuck with the
> > combination of options "-s/-f/-z" and "-s/-e/-f/-z" doesn't look good
> > for an end user.
>
> I agree that it's not right, but I don't think the solution is to ban
> the combination. I think what we should do is change the behavior to
> make the combination potentially useful, so that it waits until program
> termination and print the summary then. Consider "strace -c" as a
> precedent: it will also "become stuck" until you kill it, and then it'll
> print a nice table, just like the pg_waldump -z gives you.
>
> I think I would even have had occasion to use this as a feature in the
> past ...

Hm. So, the pg_waldump can have handlers for SIGINT, SIGTERM, SIGQUIT
and then it should emit the computed stats in those handlers the
comobinations - "-s/-f/-z" and "-s/-e/-f/-z". I'm okay with this
behaviour. Michael Paquier had suggested the same upthread. If okay, I
will work on that patch.

Thoughts?

Regards,
Bharath Rupireddy.