Re: Progress reporting for pg_verify_checksums

On Tue, Sep 4, 2018 at 2:21 AM Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> wrote:
> On 2018-Sep-01, Fabien COELHO wrote:
> > > If -P was forgotten and pg_verify_checksums operates on a large cluster,
> > > the caller can send SIGUSR1 to pg_verify_checksums to turn progress
> > > status reporting on during runtime.
> >
> > Hmmm. I cannot say I like the signal feature much. Would it make sense for
> > the progress to be on by default, and to have a quiet option instead?
>
> Hmm, I recall this technique being used elsewhere and is sometimes
> useful. Can't remember where though -- by manpages, it's not rsync nor
> pv ...

On BSD-derived systems including macOS, you can hit ^T to deliver
SIGINFO to the foreground process (much like ^C delivers SIGINT).
Many well behaved programs including rsync (at least on FreeBSD) then
show you some kind of progress or status report:

munro(at)asterix $ sleep 60
load: 0.11 cmd: sleep 62234 [nanslp] 1.22r 0.00u 0.00s 0% 2032k
sleep: about 58 second(s) left out of the original 60

I've contemplated various crackpot ideas about teaching psql to show
information about what my backend is doing when I hit ^T (perhaps via
a second connection, similar to the way it cancels queries?)...

There was an interesting thread[1] about dumping various things from
backends on (multiplexed) SIGUSR1. Also if memory serves, JVMs also
dump internal stuff when you signal them, so you can confirm that they
really did eat all 64GB of your RAM. But none of these things are
examples of enabling/disabling an on-going status reporting mode,
which is perhaps what you meant, they're more like one-off pokes to
dump information.

[1] https://www.postgresql.org/message-id/flat/20140623101501.GN16260%40awork2.anarazel.de

--
Thomas Munro
http://www.enterprisedb.com