Merge branch 'master' into issue-10417-1

Co-authored-by: cubic-dev-ai[bot] <191113872+cubic-dev-ai[bot]@users.noreply.github.com>
Signed-off-by: JAYICE <jayice.zhou@qq.com>

app/vmselect/promql/exec_test.go

@@ -4842,6 +4842,137 @@ func TestExecSuccess(t *testing.T) {
 		resultExpected := []netstorage.Result{}
 		f(q, resultExpected)
 	})
+	// buckets that are consecutively empty at left and right ends will not be preserved.
+	t.Run(`buckets_limit(trim_zero_preserve_empty_when_limit_not_reached)`, func(t *testing.T) {
+		t.Parallel()
+		q := `sort(buckets_limit(3, (
+			alias(label_set(36, "le", "+Inf"), "metric"),
+			alias(label_set(36, "le", "25"), "metric"),
+			alias(label_set(36, "le", "21"), "metric"),
+			alias(label_set(36, "le", "19"), "metric"),
+			alias(label_set(36, "le", "18"), "metric"),
+			alias(label_set(36, "le", "17"), "metric"),
+			alias(label_set(36, "le", "16"), "metric"),
+			alias(label_set(27, "le", "12"), "metric"),
+			alias(label_set(14, "le", "9"), "metric"),
+			alias(label_set(0, "le", "6"), "metric"),
+			alias(label_set(0, "le", "1"), "metric"),
+			)))`
+		r1 := netstorage.Result{
+			MetricName: metricNameExpected,
+			Values:     []float64{14, 14, 14, 14, 14, 14},
+			Timestamps: timestampsExpected,
+		}
+		r1.MetricName.MetricGroup = []byte("metric")
+		r1.MetricName.Tags = []storage.Tag{
+			{
+				Key:   []byte("le"),
+				Value: []byte("9"),
+			},
+		}
+		r2 := netstorage.Result{
+			MetricName: metricNameExpected,
+			Values:     []float64{27, 27, 27, 27, 27, 27},
+			Timestamps: timestampsExpected,
+		}
+		r2.MetricName.MetricGroup = []byte("metric")
+		r2.MetricName.Tags = []storage.Tag{
+			{
+				Key:   []byte("le"),
+				Value: []byte("12"),
+			},
+		}
+		r3 := netstorage.Result{
+			MetricName: metricNameExpected,
+			Values:     []float64{36, 36, 36, 36, 36, 36},
+			Timestamps: timestampsExpected,
+		}
+		r3.MetricName.MetricGroup = []byte("metric")
+		r3.MetricName.Tags = []storage.Tag{
+			{
+				Key:   []byte("le"),
+				Value: []byte("16"),
+			},
+		}
+		resultExpected := []netstorage.Result{r1, r2, r3}
+		f(q, resultExpected)
+	})
+
+	// the number of non-empty bucket doesn't reach the given "limit", so some empty buckets will be preserved
+	t.Run(`buckets_limit(trim_zero)`, func(t *testing.T) {
+		t.Parallel()
+		q := `sort(buckets_limit(5, (
+			alias(label_set(36, "le", "18"), "metric"),
+			alias(label_set(36, "le", "17"), "metric"),
+			alias(label_set(36, "le", "16"), "metric"),
+			alias(label_set(27, "le", "12"), "metric"),
+			alias(label_set(14, "le", "9"), "metric"),
+			alias(label_set(0, "le", "6"), "metric"),
+			alias(label_set(0, "le", "1"), "metric"),
+			)))`
+		r1 := netstorage.Result{
+			MetricName: metricNameExpected,
+			Values:     []float64{0, 0, 0, 0, 0, 0},
+			Timestamps: timestampsExpected,
+		}
+		r1.MetricName.MetricGroup = []byte("metric")
+		r1.MetricName.Tags = []storage.Tag{
+			{
+				Key:   []byte("le"),
+				Value: []byte("6"),
+			},
+		}
+		r2 := netstorage.Result{
+			MetricName: metricNameExpected,
+			Values:     []float64{14, 14, 14, 14, 14, 14},
+			Timestamps: timestampsExpected,
+		}
+		r2.MetricName.MetricGroup = []byte("metric")
+		r2.MetricName.Tags = []storage.Tag{
+			{
+				Key:   []byte("le"),
+				Value: []byte("9"),
+			},
+		}
+		r3 := netstorage.Result{
+			MetricName: metricNameExpected,
+			Values:     []float64{27, 27, 27, 27, 27, 27},
+			Timestamps: timestampsExpected,
+		}
+		r3.MetricName.MetricGroup = []byte("metric")
+		r3.MetricName.Tags = []storage.Tag{
+			{
+				Key:   []byte("le"),
+				Value: []byte("12"),
+			},
+		}
+		r4 := netstorage.Result{
+			MetricName: metricNameExpected,
+			Values:     []float64{36, 36, 36, 36, 36, 36},
+			Timestamps: timestampsExpected,
+		}
+		r4.MetricName.MetricGroup = []byte("metric")
+		r4.MetricName.Tags = []storage.Tag{
+			{
+				Key:   []byte("le"),
+				Value: []byte("16"),
+			},
+		}
+		r5 := netstorage.Result{
+			MetricName: metricNameExpected,
+			Values:     []float64{36, 36, 36, 36, 36, 36},
+			Timestamps: timestampsExpected,
+		}
+		r5.MetricName.MetricGroup = []byte("metric")
+		r5.MetricName.Tags = []storage.Tag{
+			{
+				Key:   []byte("le"),
+				Value: []byte("17"),
+			},
+		}
+		resultExpected := []netstorage.Result{r1, r2, r3, r4, r5}
+		f(q, resultExpected)
+	})
 	t.Run(`buckets_limit(unused)`, func(t *testing.T) {
 		t.Parallel()
 		q := `sort(buckets_limit(5, (
@@ -6228,50 +6359,6 @@ func TestExecSuccess(t *testing.T) {
 		resultExpected := []netstorage.Result{r1, r2, r3, r4, r5, r6, r7}
 		f(q, resultExpected)
 	})
-	t.Run(`sum(histogram_over_time) by (vmrange)`, func(t *testing.T) {
-		t.Parallel()
-		q := `sort_by_label(
-			buckets_limit(
-				3,
-				sum(histogram_over_time(alias(label_set(rand(0)*1.3+1.1, "foo", "bar"), "xxx")[200s:5s])) by (vmrange)
-			), "le"
-		)`
-		r1 := netstorage.Result{
-			MetricName: metricNameExpected,
-			Values:     []float64{40, 40, 40, 40, 40, 40},
-			Timestamps: timestampsExpected,
-		}
-		r1.MetricName.Tags = []storage.Tag{
-			{
-				Key:   []byte("le"),
-				Value: []byte("+Inf"),
-			},
-		}
-		r2 := netstorage.Result{
-			MetricName: metricNameExpected,
-			Values:     []float64{0, 0, 0, 0, 0, 0},
-			Timestamps: timestampsExpected,
-		}
-		r2.MetricName.Tags = []storage.Tag{
-			{
-				Key:   []byte("le"),
-				Value: []byte("1.000e+00"),
-			},
-		}
-		r3 := netstorage.Result{
-			MetricName: metricNameExpected,
-			Values:     []float64{40, 40, 40, 40, 40, 40},
-			Timestamps: timestampsExpected,
-		}
-		r3.MetricName.Tags = []storage.Tag{
-			{
-				Key:   []byte("le"),
-				Value: []byte("2.448e+00"),
-			},
-		}
-		resultExpected := []netstorage.Result{r1, r2, r3}
-		f(q, resultExpected)
-	})
 	t.Run(`sum(histogram_over_time)`, func(t *testing.T) {
 		t.Parallel()
 		q := `sum(histogram_over_time(alias(label_set(rand(0)*1.3+1.1, "foo", "bar"), "xxx")[200s:5s]))`

app/vmselect/promql/transform.go

@@ -461,6 +461,41 @@ func transformBucketsLimit(tfa *transformFuncArg) ([]*timeseries, error) {
 				prevValue = value
 			}
 		}
+
+		// Remove buckets that are consecutively empty at left and right ends to obtain more accurate max and min values.
+		// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/10417.
+		epsilon := 1e-9
+		l := 0
+		r := len(leGroup) - 1
+		trimLeft := true
+		for r-l+1 > limit {
+			leftHits := math.Abs(leGroup[l].hits)
+			rightHits := math.Abs(leGroup[r].hits)
+			leftEmpty := !math.IsNaN(leftHits) && leftHits <= epsilon
+			rightEmpty := !math.IsNaN(rightHits) && rightHits <= epsilon
+			if !leftEmpty && !rightEmpty {
+				break
+			}
+			if trimLeft {
+				if leftHits < epsilon {
+					l++
+				}
+				// switch the trim pointer to the right side if needed
+				if rightHits < epsilon {
+					trimLeft = false
+				}
+			} else {
+				if rightHits < epsilon {
+					r--
+				}
+				// switch the trim pointer to the left side if needed
+				if leftHits < epsilon {
+					trimLeft = true
+				}
+			}
+		}
+		leGroup = leGroup[l : r+1]
+
 		for len(leGroup) > limit {
 			// Preserve the first and the last bucket for better accuracy for min and max values
 			xxMinIdx := 1

docs/victoriametrics/changelog/CHANGELOG.md

@@ -41,6 +41,7 @@ See also [LTS releases](https://docs.victoriametrics.com/victoriametrics/lts-rel
 * BUGFIX: All VictoriaMetrics components: Fix an issue where `unsupported` metric metadata type was exposed for summaries and quantiles if a summary wasn't updated within a certain time window. See [metrics#120](https://github.com/VictoriaMetrics/metrics/issues/120) and [metrics#121](https://github.com/VictoriaMetrics/metrics/pull/121).
 * BUGFIX: [vmauth](https://docs.victoriametrics.com/victoriametrics/vmauth/): align request body buffering flags - `maxRequestBodySizeToRetry` and `requestBufferSize` to the same `16KB` value. Allow disabling request buffering by setting `requestBufferSize=0`. See [#10675](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/10675)
 * BUGFIX: [vmagent](https://docs.victoriametrics.com/victoriametrics/vmagent/): fix `scrape_series_added` metric to update only on successful scrapes, aligning its behavior with Prometheus. See [#10653](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/10653).
+* BUGFIX: [MetricsQL](https://docs.victoriametrics.com/victoriametrics/metricsql/): improve the selection algorithm of [buckets_limit](https://docs.victoriametrics.com/victoriametrics/metricsql/#buckets_limit) to remove consecutive empty buckets at the beginning and end to obtain more accurate min and max values. See [#10417](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/10417).
 
 ## [v1.139.0](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v1.139.0)