Hi út 16. 2. 2021 v 2:49 odesílatel Thomas Munro <thomas.mu...@gmail.com> napsal:
> On Fri, Jan 8, 2021 at 10:36 PM Pavel Stehule <pavel.steh...@gmail.com> > wrote: > > ne 19. 4. 2020 v 19:27 odesílatel Pavel Stehule <pavel.steh...@gmail.com> > napsal: > >> last week I finished pspg 3.0 https://github.com/okbob/pspg . pspg now > supports pipes, named pipes very well. Today the pspg can be used as pager > for output of \watch command. Sure, psql needs attached patch. > >> > >> I propose new psql environment variable PSQL_WATCH_PAGER. When this > variable is not empty, then \watch command starts specified pager, and > redirect output to related pipe. When pipe is closed - by pager, then > \watch cycle is leaved. > >> > >> If you want to test proposed feature, you need a pspg with > cb4114f98318344d162a84b895a3b7f8badec241 commit. > >> > >> Then you can set your env > >> > >> export PSQL_WATCH_PAGER="pspg --stream" > >> psql > >> > >> SELECT * FROM pg_stat_database; > >> \watch 1 > >> > >> Comments, notes? > > I tried this out with pspg 4.1 from my package manager. It seems > really useful, especially for demos. I like it! > Thank you :) > * Set up rendering options, in particular, disable the pager, > because > * nobody wants to be prompted while watching the output of > 'watch'. > */ > - myopt.topt.pager = 0; > + if (!pagerpipe) > + myopt.topt.pager = 0; > > Obsolete comment. > > +static bool sigpipe_received = false; > > This should be "static volatile sig_atomic_t", and I suppose our > convention name for that variable would be got_SIGPIPE. Would it be > possible to ignore SIGPIPE instead, and then rely on another way of > knowing that the pager has quit? But... hmm: > > - long s = Min(i, 1000L); > + long s = Min(i, pagerpipe ? 100L : > 1000L); > > I haven't studied this (preexisting) polling loop, but I don't like > it. I understand that it's there because on some systems, pg_usleep() > won't wake up for SIGINT (^C), but now it's being used for a secondary > purpose, that I haven't fully understood. After I quit pspg (by > pressing q) while running \watch 10, I have to wait until the end of a > 10 second cycle before it tries to write to the pipe again, unless I > also press ^C. I feel like it has to be possible to achieve "precise" > behaviour somehow when you quit; maybe something like waiting for > readiness on the pager's stderr, or something like that -- I haven't > thought hard about this and I admit that I have no idea how this works > on Windows. > I'll look there. > Sometimes I see a message like this after I quit pspg: > > postgres=# \watch 10 > input stream was closed > This is a pspg's message. It's a little bit strange, because this message comes from event reading, and in the end, the pspg doesn't read events. So it looks like the pspg issue, and I have to check it. I have one question - now, the pspg has to do complex heuristics to detect an start and an end of data in an stream. Can we, in this case (when PSQL_WATCH_PAGER is active), use invisible chars STX and ETX or maybe ETB? It can be a special \pset option. Surely, the detection of these chars should be much more robust than current pspg's heuristics. Regards Pavel
