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Add PSQL_WATCH_PAGER for psql's \watch command.

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Allow a pager to be used by the \watch command.  This works but isn't
very useful with traditional pagers like "less", so use a different
environment variable.  The popular open source tool "pspg" (also by
Pavel) knows how to display the output if you set PSQL_WATCH_PAGER="pspg
--stream".

To make \watch react quickly when the user quits the pager or presses
^C, and also to increase the accuracy of its timing and decrease the
rate of useless context switches, change the main loop of the \watch
command to use sigwait() rather than a sleeping/polling loop, on Unix.

Supported on Unix only for now (like pspg).

Author: Pavel Stehule <pavel.stehule@gmail.com>
Author: Thomas Munro <thomas.munro@gmail.com>
Discussion: https://postgr.es/m/CAFj8pRBfzUUPz-3gN5oAzto9SDuRSq-TQPfXU_P6h0L7hO%2BEhg%40mail.gmail.com
This commit is contained in:
Thomas Munro
2021-07-13 11:13:48 +12:00
parent f014b1b9bb
commit 7c09d2797e
6 changed files with 184 additions and 15 deletions
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6
src/bin/psql/help.c
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@ -347,7 +347,7 @@ helpVariables(unsigned short int pager)
* Windows builds currently print one more line than non-Windows builds.
* Using the larger number is fine.
*/
output = PageOutput(158, pager ? &(pset.popt.topt) : NULL);
output = PageOutput(160, pager ? &(pset.popt.topt) : NULL);
fprintf(output, _("List of specially treated variables\n\n"));
@ -505,6 +505,10 @@ helpVariables(unsigned short int pager)
" alternative location for the command history file\n"));
fprintf(output, _(" PSQL_PAGER, PAGER\n"
" name of external pager program\n"));
#ifndef WIN32
fprintf(output, _(" PSQL_WATCH_PAGER\n"
" name of external pager program used for \\watch\n"));
#endif
fprintf(output, _(" PSQLRC\n"
" alternative location for the user's .psqlrc file\n"));
fprintf(output, _(" SHELL\n"