From: Fujii Masao <fujii@postgresql.org>
Date: Fri, 24 Apr 2026 03:11:40 +0000 (+0900)
Subject: pg_test_timing: store timing deltas in int64
X-Git-Url: http://git.ipfire.org/gitweb/?a=commitdiff_plain;h=863c4b827d92879dbd526a43a23c33fa9bd23b4f;p=thirdparty%2Fpostgresql.git

pg_test_timing: store timing deltas in int64

Commit 0b096e379e6 changed pg_test_timing to measure timing
differences in nanoseconds instead of microseconds, but the resulting
deltas continued to be stored in int32.

That can overflow for large gaps (for example, values greater than about
2.14 seconds in nanoseconds), leading to truncation or incorrect output.

This commit fixes the issue by storing measured timing deltas in int64.
This prevents overflow for large values and better matches
nanosecond-resolution measurements.

Author: Chao Li <lic@highgo.com>
Reviewed-by: Lukas Fittl <lukas@fittl.com>
Reviewed-by: Xiaopeng Wang <wxp_728@163.com>
Reviewed-by: Fujii Masao <masao.fujii@gmail.com>
Discussion: https://postgr.es/m/F780CEEB-A237-4302-9F55-60E9D8B6533D@gmail.com
---

diff --git a/src/bin/pg_test_timing/pg_test_timing.c b/src/bin/pg_test_timing/pg_test_timing.c
index 944b25df1f2..5649c3e459f 100644
--- a/src/bin/pg_test_timing/pg_test_timing.c
+++ b/src/bin/pg_test_timing/pg_test_timing.c
@@ -18,14 +18,14 @@ static unsigned int test_duration = 3;
 static double max_rprct = 99.99;
 
 /* record duration in powers of 2 nanoseconds */
-static long long int histogram[32];
+static long long int histogram[64];
 
 /* record counts of first 10K durations directly */
 #define NUM_DIRECT 10000
 static long long int direct_histogram[NUM_DIRECT];
 
 /* separately record highest observed duration */
-static int32 largest_diff;
+static int64 largest_diff;
 static long long int largest_diff_count;
 
 
@@ -262,8 +262,8 @@ test_timing(unsigned int duration, TimingClockSourceType source, bool fast_timin
 
 	while (INSTR_TIME_GT(end_time, cur))
 	{
-		int32		diff,
-					bits;
+		int64		diff;
+		int32		bits;
 		instr_time	diff_time;
 
 		prev = cur;
@@ -281,13 +281,17 @@ test_timing(unsigned int duration, TimingClockSourceType source, bool fast_timin
 		if (unlikely(diff < 0))
 		{
 			fprintf(stderr, _("Detected clock going backwards in time.\n"));
-			fprintf(stderr, _("Time warp: %d ns\n"), diff);
+			fprintf(stderr, _("Time warp: " INT64_FORMAT " ns\n"), diff);
 			exit(1);
 		}
 
 		/* What is the highest bit in the time diff? */
 		if (diff > 0)
-			bits = pg_leftmost_one_pos32(diff) + 1;
+		{
+			bits = pg_leftmost_one_pos64(diff) + 1;
+			/* histogram should be defined large enough */
+			Assert(bits < lengthof(histogram));
+		}
 		else
 			bits = 0;
 
@@ -316,7 +320,7 @@ test_timing(unsigned int duration, TimingClockSourceType source, bool fast_timin
 	INSTR_TIME_SUBTRACT(end_time, start_time);
 
 	printf(_("Average loop time including overhead: %0.2f ns\n"),
-		   INSTR_TIME_GET_DOUBLE(end_time) * 1e9 / loop_count);
+		   INSTR_TIME_GET_DOUBLE(end_time) * NS_PER_S / loop_count);
 
 	return loop_count;
 }
@@ -324,7 +328,7 @@ test_timing(unsigned int duration, TimingClockSourceType source, bool fast_timin
 static void
 output(uint64 loop_count)
 {
-	int			max_bit = 31;
+	int			max_bit = lengthof(histogram) - 1;
 	const char *header1 = _("<= ns");
 	const char *header1b = _("ns");
 	const char *header2 = /* xgettext:no-c-format */ _("% of total");
@@ -342,7 +346,7 @@ output(uint64 loop_count)
 		max_bit--;
 
 	/* set minimum column widths */
-	len1 = Max(8, len1);
+	len1 = Max(19, len1);
 	len2 = Max(10, len2);
 	len3 = Max(10, len3);
 	len4 = Max(10, len4);
@@ -360,8 +364,8 @@ output(uint64 loop_count)
 		double		prct = (double) histogram[i] * 100 / loop_count;
 
 		rprct += prct;
-		printf("%*ld   %*.4f %*.4f %*lld\n",
-			   len1, (1L << i) - 1,
+		printf("%*llu   %*.4f %*.4f %*lld\n",
+			   len1, (1ULL << i) - 1,
 			   len2, prct,
 			   len3, rprct,
 			   len4, histogram[i]);
@@ -409,8 +413,8 @@ output(uint64 loop_count)
 		double		prct = (double) largest_diff_count * 100 / loop_count;
 
 		printf("...\n");
-		printf("%*d   %*.4f %*.4f %*lld\n",
-			   len1, largest_diff,
+		printf("%*lld   %*.4f %*.4f %*lld\n",
+			   len1, (long long) largest_diff,
 			   len2, prct,
 			   len3, 100.0,
 			   len4, largest_diff_count);