Add LabelQuerier.LabelValuesStream method

promql/engine_test.go

@@ -204,6 +204,10 @@ func (*errQuerier) LabelValues(context.Context, string, ...*labels.Matcher) ([]s
 	return nil, nil, nil
 }
 
+func (*errQuerier) LabelValuesStream(context.Context, string, ...*labels.Matcher) storage.LabelValues {
+	return storage.EmptyLabelValues()
+}
+
 func (*errQuerier) LabelNames(context.Context, ...*labels.Matcher) ([]string, annotations.Annotations, error) {
 	return nil, nil, nil
 }

storage/fanout_test.go

@@ -240,6 +240,10 @@ func (errQuerier) LabelValues(context.Context, string, ...*labels.Matcher) ([]st
 	return nil, nil, errors.New("label values error")
 }
 
+func (errQuerier) LabelValuesStream(context.Context, string, ...*labels.Matcher) storage.LabelValues {
+	return storage.ErrLabelValues(errors.New("label values stream error"))
+}
+
 func (errQuerier) LabelNames(context.Context, ...*labels.Matcher) ([]string, annotations.Annotations, error) {
 	return nil, nil, errors.New("label names error")
 }

storage/interface.go

@@ -126,6 +126,10 @@ func (q *MockQuerier) LabelValues(context.Context, string, ...*labels.Matcher) (
 	return nil, nil, nil
 }
 
+func (q *MockQuerier) LabelValuesStream(context.Context, string, ...*labels.Matcher) LabelValues {
+	return EmptyLabelValues()
+}
+
 func (q *MockQuerier) LabelNames(context.Context, ...*labels.Matcher) ([]string, annotations.Annotations, error) {
 	return nil, nil, nil
 }
@@ -163,6 +167,12 @@ type LabelQuerier interface {
 	// to label values of metrics matching the matchers.
 	LabelValues(ctx context.Context, name string, matchers ...*labels.Matcher) ([]string, annotations.Annotations, error)
 
+	// LabelValuesStream returns an iterator over all potential values for a label name.
+	// It is not safe to use the strings beyond the lifetime of the querier.
+	// If matchers are specified the returned result set is reduced
+	// to label values of metrics matching the matchers.
+	LabelValuesStream(ctx context.Context, name string, matchers ...*labels.Matcher) LabelValues
+
 	// LabelNames returns all the unique label names present in the block in sorted order.
 	// If matchers are specified the returned result set is reduced
 	// to label names of metrics matching the matchers.

storage/labelvalues.go

@@ -35,13 +35,15 @@ func EmptyLabelValues() LabelValues {
 
 // ListLabelValues is an iterator over a slice of label values.
 type ListLabelValues struct {
-	cur    string
-	values []string
+	cur      string
+	values   []string
+	warnings annotations.Annotations
 }
 
-func NewListLabelValues(values []string) *ListLabelValues {
+func NewListLabelValues(values []string, warnings annotations.Annotations) *ListLabelValues {
 	return &ListLabelValues{
-		values: values,
+		values:   values,
+		warnings: warnings,
 	}
 }
 
@@ -63,8 +65,8 @@ func (*ListLabelValues) Err() error {
 	return nil
 }
 
-func (*ListLabelValues) Warnings() annotations.Annotations {
-	return nil
+func (l *ListLabelValues) Warnings() annotations.Annotations {
+	return l.warnings
 }
 
 func (*ListLabelValues) Close() error {

storage/labelvalues_test.go

@@ -10,7 +10,7 @@ import (
 func TestListLabelValues(t *testing.T) {
 	t.Run("lets you traverse a slice of label values", func(t *testing.T) {
 		input := []string{"a", "b", "c", "d"}
-		it := NewListLabelValues(input)
+		it := NewListLabelValues(input, nil)
 		t.Cleanup(func() {
 			require.NoError(t, it.Close())
 		})
@@ -25,7 +25,7 @@ func TestListLabelValues(t *testing.T) {
 	})
 
 	t.Run("can be initialized with an empty slice", func(t *testing.T) {
-		it := NewListLabelValues([]string{})
+		it := NewListLabelValues([]string{}, nil)
 		t.Cleanup(func() {
 			require.NoError(t, it.Close())
 		})
@@ -36,7 +36,7 @@ func TestListLabelValues(t *testing.T) {
 	})
 
 	t.Run("can be initialized with a nil slice", func(t *testing.T) {
-		it := NewListLabelValues(nil)
+		it := NewListLabelValues(nil, nil)
 		t.Cleanup(func() {
 			require.NoError(t, it.Close())
 		})

storage/merge.go

@@ -21,13 +21,16 @@ import (
 	"math"
 	"slices"
 	"sync"
+	"unicode/utf8"
 
 	"github.com/prometheus/prometheus/model/histogram"
 	"github.com/prometheus/prometheus/model/labels"
 	"github.com/prometheus/prometheus/tsdb/chunkenc"
 	"github.com/prometheus/prometheus/tsdb/chunks"
 	tsdb_errors "github.com/prometheus/prometheus/tsdb/errors"
 	"github.com/prometheus/prometheus/util/annotations"
+
+	"github.com/bboreham/go-loser"
 )
 
 type mergeGenericQuerier struct {
@@ -220,6 +223,72 @@ func mergeStrings(a, b []string) []string {
 	return res
 }
 
+// LabelValuesStream implements LabelQuerier.
+func (q *mergeGenericQuerier) LabelValuesStream(ctx context.Context, name string, matchers ...*labels.Matcher) LabelValues {
+	if len(q.queriers) == 0 {
+		return EmptyLabelValues()
+	}
+	if len(q.queriers) == 1 {
+		return q.queriers[0].LabelValuesStream(ctx, name, matchers...)
+	}
+
+	its := make([]LabelValues, 0, len(q.queriers))
+	for _, sq := range q.queriers {
+		its = append(its, sq.LabelValuesStream(ctx, name, matchers...))
+	}
+
+	lt := loser.New(its, string(utf8.MaxRune))
+	return &mergedLabelValues{
+		lt:  lt,
+		lvs: its,
+	}
+}
+
+// mergedLabelValues is a label values iterator merging a collection of sub-iterators.
+type mergedLabelValues struct {
+	lt  *loser.Tree[string, LabelValues]
+	lvs []LabelValues
+	cur string
+}
+
+func (m *mergedLabelValues) Next() bool {
+	for m.lt.Next() {
+		// Remove duplicate entries
+		at := m.lt.At()
+		if at != m.cur {
+			m.cur = at
+			return true
+		}
+	}
+
+	return false
+}
+
+func (m *mergedLabelValues) At() string {
+	return m.cur
+}
+
+func (m *mergedLabelValues) Err() error {
+	for _, lv := range m.lvs {
+		if err := lv.Err(); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+func (m *mergedLabelValues) Warnings() annotations.Annotations {
+	var warnings annotations.Annotations
+	for _, lv := range m.lvs {
+		warnings = warnings.Merge(lv.Warnings())
+	}
+	return warnings
+}
+
+func (m *mergedLabelValues) Close() error {
+	return nil
+}
+
 // LabelNames returns all the unique label names present in all queriers in sorted order.
 func (q *mergeGenericQuerier) LabelNames(ctx context.Context, matchers ...*labels.Matcher) ([]string, annotations.Annotations, error) {
 	var (

storage/merge_test.go

@@ -1386,6 +1386,23 @@ func (m *mockGenericQuerier) LabelValues(_ context.Context, name string, matcher
 	return m.resp, m.warnings, m.err
 }
 
+func (m *mockGenericQuerier) LabelValuesStream(_ context.Context, name string, matchers ...*labels.Matcher) LabelValues {
+	m.mtx.Lock()
+	m.labelNamesRequested = append(m.labelNamesRequested, labelNameRequest{
+		name:     name,
+		matchers: matchers,
+	})
+	m.mtx.Unlock()
+
+	if m.err == nil {
+		return NewListLabelValues(m.resp, m.warnings)
+	}
+	return errLabelValues{
+		err:      m.err,
+		warnings: m.warnings,
+	}
+}
+
 func (m *mockGenericQuerier) LabelNames(context.Context, ...*labels.Matcher) ([]string, annotations.Annotations, error) {
 	m.mtx.Lock()
 	m.labelNamesCalls++
@@ -1455,8 +1472,9 @@ func TestMergeGenericQuerierWithSecondaries_ErrorHandling(t *testing.T) {
 		expectedLabels        []string
 
 		expectedWarnings annotations.Annotations
-		expectedErrs     [4]error
+		expectedErrs     [5]error
 	}{
+		{},
 		{
 			name:     "one successful primary querier",
 			queriers: []genericQuerier{&mockGenericQuerier{resp: []string{"a", "b"}, warnings: nil, err: nil}},
@@ -1482,7 +1500,7 @@ func TestMergeGenericQuerierWithSecondaries_ErrorHandling(t *testing.T) {
 		{
 			name:         "one failed primary querier",
 			queriers:     []genericQuerier{&mockGenericQuerier{warnings: nil, err: errStorage}},
-			expectedErrs: [4]error{errStorage, errStorage, errStorage, errStorage},
+			expectedErrs: [5]error{errStorage, errStorage, errStorage, errStorage, errStorage},
 		},
 		{
 			name: "one successful primary querier with successful secondaries",
@@ -1518,7 +1536,7 @@ func TestMergeGenericQuerierWithSecondaries_ErrorHandling(t *testing.T) {
 				&secondaryQuerier{genericQuerier: &mockGenericQuerier{resp: []string{"b"}, warnings: nil, err: nil}},
 				&secondaryQuerier{genericQuerier: &mockGenericQuerier{resp: []string{"c"}, warnings: nil, err: nil}},
 			},
-			expectedErrs: [4]error{errStorage, errStorage, errStorage, errStorage},
+			expectedErrs: [5]error{errStorage, errStorage, errStorage, errStorage, errStorage},
 		},
 		{
 			name: "one successful primary querier with failed secondaries",
@@ -1604,11 +1622,36 @@ func TestMergeGenericQuerierWithSecondaries_ErrorHandling(t *testing.T) {
 					require.Equal(t, []labelNameRequest{{name: "test"}}, m.labelNamesRequested)
 				}
 			})
+			t.Run("LabelValuesStream", func(t *testing.T) {
+				it := q.LabelValuesStream(ctx, "test2")
+				require.NotNil(t, it)
+				var res []string
+				for it.Next() {
+					res = append(res, it.At())
+				}
+				require.Equal(t, tcase.expectedWarnings, it.Warnings())
+				err := it.Err()
+				require.ErrorIs(t, err, tcase.expectedErrs[3], "expected error doesn't match")
+				if err != nil {
+					return
+				}
+
+				require.Equal(t, tcase.expectedLabels, res)
+
+				for _, qr := range q.queriers {
+					m := unwrapMockGenericQuerier(t, qr)
+
+					require.Equal(t, []labelNameRequest{
+						{name: "test"},
+						{name: "test2"},
+					}, m.labelNamesRequested)
+				}
+			})
 			t.Run("LabelValuesWithMatchers", func(t *testing.T) {
 				matcher := labels.MustNewMatcher(labels.MatchEqual, "otherLabel", "someValue")
-				res, w, err := q.LabelValues(ctx, "test2", matcher)
+				res, w, err := q.LabelValues(ctx, "test3", matcher)
 				require.Subset(t, tcase.expectedWarnings, w)
-				require.ErrorIs(t, err, tcase.expectedErrs[3], "expected error doesn't match")
+				require.ErrorIs(t, err, tcase.expectedErrs[4], "expected error doesn't match")
 				require.Equal(t, tcase.expectedLabels, res)
 
 				if err != nil {
@@ -1619,7 +1662,8 @@ func TestMergeGenericQuerierWithSecondaries_ErrorHandling(t *testing.T) {
 
 					require.Equal(t, []labelNameRequest{
 						{name: "test"},
-						{name: "test2", matchers: []*labels.Matcher{matcher}},
+						{name: "test2"},
+						{name: "test3", matchers: []*labels.Matcher{matcher}},
 					}, m.labelNamesRequested)
 				}
 			})

storage/noop.go

@@ -35,6 +35,10 @@ func (noopQuerier) LabelValues(context.Context, string, ...*labels.Matcher) ([]s
 	return nil, nil, nil
 }
 
+func (noopQuerier) LabelValuesStream(context.Context, string, ...*labels.Matcher) LabelValues {
+	return EmptyLabelValues()
+}
+
 func (noopQuerier) LabelNames(context.Context, ...*labels.Matcher) ([]string, annotations.Annotations, error) {
 	return nil, nil, nil
 }
@@ -58,6 +62,10 @@ func (noopChunkQuerier) LabelValues(context.Context, string, ...*labels.Matcher)
 	return nil, nil, nil
 }
 
+func (noopChunkQuerier) LabelValuesStream(context.Context, string, ...*labels.Matcher) LabelValues {
+	return EmptyLabelValues()
+}
+
 func (noopChunkQuerier) LabelNames(context.Context, ...*labels.Matcher) ([]string, annotations.Annotations, error) {
 	return nil, nil, nil
 }

storage/remote/read.go

@@ -209,12 +209,18 @@ func (q querier) addExternalLabels(ms []*labels.Matcher) ([]*labels.Matcher, []s
 	return ms, names
 }
 
-// LabelValues implements storage.Querier and is a noop.
+// LabelValues implements storage.LabelQuerier and is a noop.
 func (q *querier) LabelValues(context.Context, string, ...*labels.Matcher) ([]string, annotations.Annotations, error) {
 	// TODO: Implement: https://github.com/prometheus/prometheus/issues/3351
 	return nil, nil, errors.New("not implemented")
 }
 
+// LabelValuesStream implements storage.LabelQuerier and is a noop.
+func (q *querier) LabelValuesStream(context.Context, string, ...*labels.Matcher) storage.LabelValues {
+	// TODO: Implement: https://github.com/prometheus/prometheus/issues/3351
+	return storage.ErrLabelValues(errors.New("not implemented"))
+}
+
 // LabelNames implements storage.Querier and is a noop.
 func (q *querier) LabelNames(context.Context, ...*labels.Matcher) ([]string, annotations.Annotations, error) {
 	// TODO: Implement: https://github.com/prometheus/prometheus/issues/3351

storage/secondary.go

@@ -57,6 +57,28 @@ func (s *secondaryQuerier) LabelValues(ctx context.Context, name string, matcher
 	return vals, w, nil
 }
 
+func (s *secondaryQuerier) LabelValuesStream(ctx context.Context, name string, matchers ...*labels.Matcher) LabelValues {
+	return &secondaryLabelValues{
+		s.genericQuerier.LabelValuesStream(ctx, name, matchers...),
+	}
+}
+
+type secondaryLabelValues struct {
+	LabelValues
+}
+
+func (s *secondaryLabelValues) Err() error {
+	return nil
+}
+
+func (s *secondaryLabelValues) Warnings() annotations.Annotations {
+	ws := s.LabelValues.Warnings()
+	if s.LabelValues.Err() != nil {
+		ws.Add(s.LabelValues.Err())
+	}
+	return ws
+}
+
 func (s *secondaryQuerier) LabelNames(ctx context.Context, matchers ...*labels.Matcher) ([]string, annotations.Annotations, error) {
 	names, w, err := s.genericQuerier.LabelNames(ctx, matchers...)
 	if err != nil {