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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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133
src/bin/psql/command.c
View File

@@ -13,6 +13,7 @@
#include <utime.h>
#ifndef WIN32
#include <sys/stat.h> /* for stat() */
#include <sys/time.h> /* for setitimer() */
#include <fcntl.h> /* open() flags */
#include <unistd.h> /* for geteuid(), getpid(), stat() */
#else
@@ -4894,8 +4895,17 @@ do_watch(PQExpBuffer query_buf, double sleep)
const char *strftime_fmt;
const char *user_title;
char *title;
const char *pagerprog = NULL;
FILE *pagerpipe = NULL;
int title_len;
int res = 0;
#ifndef WIN32
sigset_t sigalrm_sigchld_sigint;
sigset_t sigalrm_sigchld;
sigset_t sigint;
struct itimerval interval;
bool done = false;
#endif
if (!query_buf || query_buf->len <= 0)
{
@@ -4903,6 +4913,58 @@ do_watch(PQExpBuffer query_buf, double sleep)
return false;
}
#ifndef WIN32
sigemptyset(&sigalrm_sigchld_sigint);
sigaddset(&sigalrm_sigchld_sigint, SIGCHLD);
sigaddset(&sigalrm_sigchld_sigint, SIGALRM);
sigaddset(&sigalrm_sigchld_sigint, SIGINT);
sigemptyset(&sigalrm_sigchld);
sigaddset(&sigalrm_sigchld, SIGCHLD);
sigaddset(&sigalrm_sigchld, SIGALRM);
sigemptyset(&sigint);
sigaddset(&sigint, SIGINT);
/*
* Block SIGALRM and SIGCHLD before we start the timer and the pager (if
* configured), to avoid races. sigwait() will receive them.
*/
sigprocmask(SIG_BLOCK, &sigalrm_sigchld, NULL);
/*
* Set a timer to interrupt sigwait() so we can run the query at the
* requested intervals.
*/
interval.it_value.tv_sec = sleep_ms / 1000;
interval.it_value.tv_usec = (sleep_ms % 1000) * 1000;
interval.it_interval = interval.it_value;
if (setitimer(ITIMER_REAL, &interval, NULL) < 0)
{
pg_log_error("could not set timer: %m");
done = true;
}
#endif
/*
* For \watch, we ignore the size of the result and always use the pager
* if PSQL_WATCH_PAGER is set. We also ignore the regular PSQL_PAGER or
* PAGER environment variables, because traditional pagers probably won't
* be very useful for showing a stream of results.
*/
#ifndef WIN32
pagerprog = getenv("PSQL_WATCH_PAGER");
#endif
if (pagerprog && myopt.topt.pager)
{
disable_sigpipe_trap();
pagerpipe = popen(pagerprog, "w");
if (!pagerpipe)
/* silently proceed without pager */
restore_sigpipe_trap();
}
/*
* Choose format for timestamps. We might eventually make this a \pset
* option. In the meantime, using a variable for the format suppresses
@@ -4911,10 +4973,12 @@ do_watch(PQExpBuffer query_buf, double sleep)
strftime_fmt = "%c";
/*
* Set up rendering options, in particular, disable the pager, because
* nobody wants to be prompted while watching the output of 'watch'.
* Set up rendering options, in particular, disable the pager unless
* PSQL_WATCH_PAGER was successfully launched.
*/
myopt.topt.pager = 0;
if (!pagerpipe)
myopt.topt.pager = 0;
/*
* If there's a title in the user configuration, make sure we have room
@@ -4929,7 +4993,6 @@ do_watch(PQExpBuffer query_buf, double sleep)
{
time_t timer;
char timebuf[128];
long i;
/*
* Prepare title for output. Note that we intentionally include a
@@ -4948,7 +5011,7 @@ do_watch(PQExpBuffer query_buf, double sleep)
myopt.title = title;
/* Run the query and print out the results */
res = PSQLexecWatch(query_buf->data, &myopt);
res = PSQLexecWatch(query_buf->data, &myopt, pagerpipe);
/*
* PSQLexecWatch handles the case where we can no longer repeat the
@@ -4957,6 +5020,11 @@ do_watch(PQExpBuffer query_buf, double sleep)
if (res <= 0)
break;
if (pagerpipe && ferror(pagerpipe))
break;
#ifdef WIN32
/*
* Set up cancellation of 'watch' via SIGINT. We redo this each time
* through the loop since it's conceivable something inside
@@ -4967,12 +5035,10 @@ do_watch(PQExpBuffer query_buf, double sleep)
/*
* Enable 'watch' cancellations and wait a while before running the
* query again. Break the sleep into short intervals (at most 1s)
* since pg_usleep isn't interruptible on some platforms.
* query again. Break the sleep into short intervals (at most 1s).
*/
sigint_interrupt_enabled = true;
i = sleep_ms;
while (i > 0)
for (long i = sleep_ms; i > 0;)
{
long s = Min(i, 1000L);
@@ -4982,8 +5048,57 @@ do_watch(PQExpBuffer query_buf, double sleep)
i -= s;
}
sigint_interrupt_enabled = false;
#else
/* sigwait() will handle SIGINT. */
sigprocmask(SIG_BLOCK, &sigint, NULL);
if (cancel_pressed)
done = true;
/* Wait for SIGINT, SIGCHLD or SIGALRM. */
while (!done)
{
int signal_received;
if (sigwait(&sigalrm_sigchld_sigint, &signal_received) < 0)
{
/* Some other signal arrived? */
if (errno == EINTR)
continue;
else
{
pg_log_error("could not wait for signals: %m");
done = true;
break;
}
}
/* On ^C or pager exit, it's time to stop running the query. */
if (signal_received == SIGINT || signal_received == SIGCHLD)
done = true;
/* Otherwise, we must have SIGALRM. Time to run the query again. */
break;
}
/* Unblock SIGINT so that slow queries can be interrupted. */
sigprocmask(SIG_UNBLOCK, &sigint, NULL);
if (done)
break;
#endif
}
if (pagerpipe)
{
pclose(pagerpipe);
restore_sigpipe_trap();
}
#ifndef WIN32
/* Disable the interval timer. */
memset(&interval, 0, sizeof(interval));
setitimer(ITIMER_REAL, &interval, NULL);
/* Unblock SIGINT, SIGCHLD and SIGALRM. */
sigprocmask(SIG_UNBLOCK, &sigalrm_sigchld_sigint, NULL);
#endif
pg_free(title);
return (res >= 0);
}