app/vmselect: make sorting for query result similar to Prometheus (#1647)

* app/vmselect: make sorting for query result similar to Prometheus

Updated sorting allows to get the order of series in result similar or equal
to what Prometheus returns.
The change is needed for compatibility reasons.

* Update app/vmselect/promql/exec_test.go

Co-authored-by: Aliaksandr Valialkin <valyala@victoriametrics.com>

app/vmselect/promql/exec.go

@@ -95,7 +95,7 @@ func timeseriesToResult(tss []*timeseries, maySort bool) ([]netstorage.Result, e
 	m := make(map[string]struct{}, len(tss))
 	bb := bbPool.Get()
 	for i, ts := range tss {
-		bb.B = marshalMetricNameSorted(bb.B[:0], &ts.MetricName)
+		bb.B = metricNameToBytes(bb.B[:0], &ts.MetricName)
 		if _, ok := m[string(bb.B)]; ok {
 			return nil, fmt.Errorf(`duplicate output timeseries: %s`, stringMetricName(&ts.MetricName))
 		}

app/vmselect/promql/exec_test.go

@@ -1,6 +1,7 @@
 package promql
 
 import (
+	"fmt"
 	"testing"
 	"time"
 
@@ -6964,7 +6965,8 @@ func TestExecSuccess(t *testing.T) {
 				Value: []byte("10"),
 			},
 		}
-		resultExpected := []netstorage.Result{r1, r2, r3, r4}
+		// expected sorted output for strings 1, 10, 2, 3
+		resultExpected := []netstorage.Result{r1, r4, r2, r3}
 		f(q, resultExpected)
 	})
 	t.Run(`count_values without (baz)`, func(t *testing.T) {
@@ -7018,6 +7020,44 @@ func TestExecSuccess(t *testing.T) {
 		resultExpected := []netstorage.Result{r1, r2, r3}
 		f(q, resultExpected)
 	})
+	t.Run(`result sorting`, func(t *testing.T) {
+		t.Parallel()
+		q := `label_set(1, "instance", "localhost:1001", "type", "free")
+			or label_set(1, "instance", "localhost:1001", "type", "buffers")
+			or label_set(1, "instance", "localhost:1000", "type", "buffers")
+			or label_set(1, "instance", "localhost:1000", "type", "free")
+`
+		r1 := netstorage.Result{
+			MetricName: metricNameExpected,
+			Values:     []float64{1, 1, 1, 1, 1, 1},
+			Timestamps: timestampsExpected,
+		}
+		testAddLabels(t, &r1.MetricName,
+			"instance", "localhost:1000", "type", "buffers")
+		r2 := netstorage.Result{
+			MetricName: metricNameExpected,
+			Values:     []float64{1, 1, 1, 1, 1, 1},
+			Timestamps: timestampsExpected,
+		}
+		testAddLabels(t, &r2.MetricName,
+			"instance", "localhost:1000", "type", "free")
+		r3 := netstorage.Result{
+			MetricName: metricNameExpected,
+			Values:     []float64{1, 1, 1, 1, 1, 1},
+			Timestamps: timestampsExpected,
+		}
+		testAddLabels(t, &r3.MetricName,
+			"instance", "localhost:1001", "type", "buffers")
+		r4 := netstorage.Result{
+			MetricName: metricNameExpected,
+			Values:     []float64{1, 1, 1, 1, 1, 1},
+			Timestamps: timestampsExpected,
+		}
+		testAddLabels(t, &r4.MetricName,
+			"instance", "localhost:1001", "type", "free")
+		resultExpected := []netstorage.Result{r1, r2, r3, r4}
+		f(q, resultExpected)
+	})
 }
 
 func TestExecError(t *testing.T) {
@@ -7305,3 +7345,16 @@ func testMetricNamesEqual(t *testing.T, mn, mnExpected *storage.MetricName, pos
 		}
 	}
 }
+
+func testAddLabels(t *testing.T, mn *storage.MetricName, labels ...string) {
+	t.Helper()
+	if len(labels)%2 > 0 {
+		t.Fatalf("uneven number of labels passed: %v", labels)
+	}
+	for i := 0; i < len(labels); i += 2 {
+		mn.Tags = append(mn.Tags, storage.Tag{
+			Key:   []byte(labels[i]),
+			Value: []byte(labels[i+1]),
+		})
+	}
+}

app/vmselect/promql/timeseries.go

@@ -318,6 +318,18 @@ func marshalMetricTagsFast(dst []byte, tags []storage.Tag) []byte {
 	return dst
 }
 
+func metricNameToBytes(dst []byte, mn *storage.MetricName) []byte {
+	dst = marshalBytesFast(dst, mn.MetricGroup)
+	sortMetricTags(mn.Tags)
+	for i := range mn.Tags {
+		tag := &mn.Tags[i]
+		dst = append(dst, tag.Key...)
+		dst = append(dst, tag.Value...)
+		dst = append(dst, ","...)
+	}
+	return dst
+}
+
 func marshalMetricNameSorted(dst []byte, mn *storage.MetricName) []byte {
 	// Do not marshal AccountID and ProjectID, since they are unused.
 	dst = marshalBytesFast(dst, mn.MetricGroup)