postgres.git / summary / log / commit / refs

commit    8a6170860c83d3f44b7d97193a2c23539c24f76d
Author:   Michael Paquier <michael@paquier.xyz>
Date:     Mon Oct 14 03:27:57 2024 +0000
First released in: 18.0, 16.5, 17.1

    psql: Fix \watch when using interval values less than 1ms
    
    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
    6f9ee74d45aa, 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


 src/bin/psql/command.c      | 11 ++++++++---
 src/bin/psql/t/001_basic.pl | 10 ++++++++--
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 4d2c81aa753..f8a21a79c7d 100644
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -5231,6 +5231,10 @@ 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)
@@ -5356,10 +5360,10 @@ 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 */
@@ -5380,7 +5384,8 @@ 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
diff --git a/src/bin/psql/t/001_basic.pl b/src/bin/psql/t/001_basic.pl
index 5f2f4541af0..bd4fdd2030a 100644
--- a/src/bin/psql/t/001_basic.pl
+++ b/src/bin/psql/t/001_basic.pl
@@ -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(


[parent: 54889ea64baa]