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psql: Fix \watch when using interval values less than 1ms

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Attempting to use an interval of time less than 1ms would cause \watch
to hang.  This was confusing, so let's change the logic so as an
interval lower than 1ms behaves the same as 0.

Comments are added to mention that the internals of do_watch() had
better rely on "sleep_ms", the interval value in milliseconds.  While on
it, this commit adds a test to check the behavior of interval values
less than 1ms.

\watch hanging for interval values less than 1ms existed before
6f9ee74d45, that has changed the code to support an interval value of
0.

Reported-by: Heikki Linnakangas
Author: Andrey M. Borodin, Michael Paquier
Discussion: https://postgr.es/m/88445e0e-3156-4b9d-afae-9a1a7b1631f6@iki.fi
Backpatch-through: 16
This commit is contained in:
Michael Paquier 2024-10-14 12:27:51 +09:00
parent 35a015a600
commit 9f34cae142
2 changed files with 16 additions and 5 deletions
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11
src/bin/psql/command.c
View File

@ -5359,6 +5359,10 @@ do_shell(const char *command)
*
* We break this out of exec_command to avoid having to plaster "volatile"
* onto a bunch of exec_command's variables to silence stupider compilers.
*
* "sleep" is the amount of time to sleep during each loop, measured in
* seconds. The internals of this function should use "sleep_ms" for
* precise sleep time calculations.
*/
static bool
do_watch(PQExpBuffer query_buf, double sleep, int iter, int min_rows)
@ -5484,10 +5488,10 @@ do_watch(PQExpBuffer query_buf, double sleep, int iter, int min_rows)
if (user_title)
snprintf(title, title_len, _("%s\t%s (every %gs)\n"),
user_title, timebuf, sleep);
user_title, timebuf, sleep_ms / 1000.0);
else
snprintf(title, title_len, _("%s (every %gs)\n"),
timebuf, sleep);
timebuf, sleep_ms / 1000.0);
myopt.title = title;
/* Run the query and print out the result */
@ -5508,7 +5512,8 @@ do_watch(PQExpBuffer query_buf, double sleep, int iter, int min_rows)
if (pagerpipe && ferror(pagerpipe))
break;
if (sleep == 0)
/* Tight loop, no wait needed */
if (sleep_ms == 0)
continue;
#ifdef WIN32

10
src/bin/psql/t/001_basic.pl
View File

@ -352,8 +352,14 @@ psql_like(
# Check \watch
# Note: the interval value is parsed with locale-aware strtod()
psql_like($node, sprintf('SELECT 1 \watch c=3 i=%g', 0.01),
qr/1\n1\n1/, '\watch with 3 iterations');
psql_like(
$node, sprintf('SELECT 1 \watch c=3 i=%g', 0.01),
qr/1\n1\n1/, '\watch with 3 iterations, interval of 0.01');
# Sub-millisecond wait works, equivalent to 0.
psql_like(
$node, sprintf('SELECT 1 \watch c=3 i=%g', 0.0001),
qr/1\n1\n1/, '\watch with 3 iterations, interval of 0.0001');
# Check \watch minimum row count
psql_fails_like(