On Fri, Jan 8, 2021 at 10:36 PM Pavel Stehule <pavel.stehule@gmail.com> wrote:
> ne 19. 4. 2020 v 19:27 odesílatel Pavel Stehule <pavel.stehule@gmail.com> napsal:
>> last week I finished pspg 3.0 https://github.com/okbob/pspg . pspg now supports pipes, named pipes very well. Today
thepspg 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
startsspecified 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!
* 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.
Sometimes I see a message like this after I quit pspg:
postgres=# \watch 10
input stream was closed
