telemetry: fix the integer quantization

The code was previously quantizing 100 to 10, and only
101 and higher to 100. This patch fixes it.

Additionally, this code ensures that negative values also get
quantized. This change does not impact any caller for now (there is no
caller that expects negative value) but will be used in an upcoming
setting telemetry change.

Release justification: low risk, high benefit changes to existing functionality

Release note: None

pkg/server/telemetry/features.go

@@ -12,6 +12,7 @@ package telemetry
 
 import (
 	"fmt"
+	"math"
 	"sync/atomic"
 
 	"github.com/cockroachdb/cockroach/pkg/sql/pgwire/pgcode"
@@ -27,16 +28,22 @@ import (
 // raw numbers.
 // The numbers 0-10 are reported unchanged.
 func Bucket10(num int64) int64 {
-	if num <= 0 {
-		return 0
+	if num == math.MinInt64 {
+		// This is needed to prevent overflow in the negation below.
+		return -1000000000000000000
+	}
+	sign := int64(1)
+	if num < 0 {
+		sign = -1
+		num = -num
 	}
 	if num < 10 {
-		return num
+		return num * sign
 	}
 	res := int64(10)
-	for ; res < 1000000000000000000 && res*10 < num; res *= 10 {
+	for ; res < 1000000000000000000 && res*10 <= num; res *= 10 {
 	}
-	return res
+	return res * sign
 }
 
 // CountBucketed counts the feature identified by prefix and the value, using

pkg/server/telemetry/features_test.go

@@ -11,6 +11,7 @@
 package telemetry_test
 
 import (
+	"math"
 	"sync"
 	"testing"
 
@@ -40,3 +41,53 @@ func TestGetCounterDoesNotRace(t *testing.T) {
 	}
 	require.Len(t, counterSet, 1)
 }
+
+// TestBucket checks integer quantization.
+func TestBucket(t *testing.T) {
+	testData := []struct {
+		input    int64
+		expected int64
+	}{
+		{0, 0},
+		{1, 1},
+		{2, 2},
+		{3, 3},
+		{4, 4},
+		{5, 5},
+		{6, 6},
+		{7, 7},
+		{8, 8},
+		{9, 9},
+		{10, 10},
+		{11, 10},
+		{20, 10},
+		{99, 10},
+		{100, 100},
+		{101, 100},
+		{200, 100},
+		{999, 100},
+		{1000, 1000},
+		{math.MaxInt64, 1000000000000000000},
+		{-1, -1},
+		{-2, -2},
+		{-3, -3},
+		{-4, -4},
+		{-5, -5},
+		{-6, -6},
+		{-7, -7},
+		{-8, -8},
+		{-9, -9},
+		{-10, -10},
+		{-11, -10},
+		{-20, -10},
+		{-100, -100},
+		{-200, -100},
+		{math.MinInt64, -1000000000000000000},
+	}
+
+	for _, tc := range testData {
+		if actual, expected := telemetry.Bucket10(tc.input), tc.expected; actual != expected {
+			t.Errorf("%d: expected %d, got %d", tc.input, expected, actual)
+		}
+	}
+}