Change LabelValuesFor() to accept index.Postings (#14280)

The only call we have to LabelValuesFor() has an index.Postings, and we
expand it to pass to this method, which will iterate over the values.

That's a waste of resources: we can iterate on the index.Postings
directly.

If there's any downstream implementation that has a slice of series,
they can always do an index.ListPostings from them: doing that is
cheaper than expanding an abstract index.Postings.

Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>

tsdb/block.go

@@ -103,9 +103,9 @@ type IndexReader interface {
 	// storage.ErrNotFound is returned as error.
 	LabelValueFor(ctx context.Context, id storage.SeriesRef, label string) (string, error)
 
-	// LabelNamesFor returns all the label names for the series referred to by IDs.
+	// LabelNamesFor returns all the label names for the series referred to by the postings.
 	// The names returned are sorted.
-	LabelNamesFor(ctx context.Context, ids ...storage.SeriesRef) ([]string, error)
+	LabelNamesFor(ctx context.Context, postings index.Postings) ([]string, error)
 
 	// Close releases the underlying resources of the reader.
 	Close() error
@@ -551,10 +551,10 @@ func (r blockIndexReader) LabelValueFor(ctx context.Context, id storage.SeriesRe
 	return r.ir.LabelValueFor(ctx, id, label)
 }
 
-// LabelNamesFor returns all the label names for the series referred to by IDs.
+// LabelNamesFor returns all the label names for the series referred to by the postings.
 // The names returned are sorted.
-func (r blockIndexReader) LabelNamesFor(ctx context.Context, ids ...storage.SeriesRef) ([]string, error) {
-	return r.ir.LabelNamesFor(ctx, ids...)
+func (r blockIndexReader) LabelNamesFor(ctx context.Context, postings index.Postings) ([]string, error) {
+	return r.ir.LabelNamesFor(ctx, postings)
 }
 
 type blockTombstoneReader struct {

tsdb/head_read.go

@@ -267,15 +267,17 @@ func (h *headIndexReader) LabelValueFor(_ context.Context, id storage.SeriesRef,
 	return value, nil
 }
 
-// LabelNamesFor returns all the label names for the series referred to by IDs.
+// LabelNamesFor returns all the label names for the series referred to by the postings.
 // The names returned are sorted.
-func (h *headIndexReader) LabelNamesFor(ctx context.Context, ids ...storage.SeriesRef) ([]string, error) {
+func (h *headIndexReader) LabelNamesFor(ctx context.Context, series index.Postings) ([]string, error) {
 	namesMap := make(map[string]struct{})
-	for _, id := range ids {
-		if ctx.Err() != nil {
+	i := 0
+	for series.Next() {
+		i++
+		if i%checkContextEveryNIterations == 0 && ctx.Err() != nil {
 			return nil, ctx.Err()
 		}
-		memSeries := h.head.series.getByID(chunks.HeadSeriesRef(id))
+		memSeries := h.head.series.getByID(chunks.HeadSeriesRef(series.At()))
 		if memSeries == nil {
 			// Series not found, this happens during compaction,
 			// when series was garbage collected after the caller got the series IDs.
@@ -285,6 +287,9 @@ func (h *headIndexReader) LabelNamesFor(ctx context.Context, ids ...storage.Seri
 			namesMap[lbl.Name] = struct{}{}
 		})
 	}
+	if err := series.Err(); err != nil {
+		return nil, err
+	}
 	names := make([]string, 0, len(namesMap))
 	for name := range namesMap {
 		names = append(names, name)

tsdb/index/index.go

@@ -1551,11 +1551,14 @@ func (r *Reader) LabelValues(ctx context.Context, name string, matchers ...*labe
 
 // LabelNamesFor returns all the label names for the series referred to by IDs.
 // The names returned are sorted.
-func (r *Reader) LabelNamesFor(ctx context.Context, ids ...storage.SeriesRef) ([]string, error) {
+func (r *Reader) LabelNamesFor(ctx context.Context, postings Postings) ([]string, error) {
 	// Gather offsetsMap the name offsetsMap in the symbol table first
 	offsetsMap := make(map[uint32]struct{})
-	for _, id := range ids {
-		if ctx.Err() != nil {
+	i := 0
+	for postings.Next() {
+		id := postings.At()
+
+		if i%checkContextEveryNIterations == 0 && ctx.Err() != nil {
 			return nil, ctx.Err()
 		}
 

tsdb/ooo_head_read.go

@@ -483,7 +483,7 @@ func (ir *OOOCompactionHeadIndexReader) LabelValueFor(context.Context, storage.S
 	return "", errors.New("not implemented")
 }
 
-func (ir *OOOCompactionHeadIndexReader) LabelNamesFor(ctx context.Context, ids ...storage.SeriesRef) ([]string, error) {
+func (ir *OOOCompactionHeadIndexReader) LabelNamesFor(ctx context.Context, postings index.Postings) ([]string, error) {
 	return nil, errors.New("not implemented")
 }
 

tsdb/querier.go

@@ -447,16 +447,7 @@ func labelNamesWithMatchers(ctx context.Context, r IndexReader, matchers ...*lab
 	if err != nil {
 		return nil, err
 	}
-
-	var postings []storage.SeriesRef
-	for p.Next() {
-		postings = append(postings, p.At())
-	}
-	if err := p.Err(); err != nil {
-		return nil, fmt.Errorf("postings for label names with matchers: %w", err)
-	}
-
-	return r.LabelNamesFor(ctx, postings...)
+	return r.LabelNamesFor(ctx, p)
 }
 
 // seriesData, used inside other iterators, are updated when we move from one series to another.

tsdb/querier_test.go

@@ -2292,13 +2292,16 @@ func (m mockIndex) LabelValueFor(_ context.Context, id storage.SeriesRef, label
 	return m.series[id].l.Get(label), nil
 }
 
-func (m mockIndex) LabelNamesFor(ctx context.Context, ids ...storage.SeriesRef) ([]string, error) {
+func (m mockIndex) LabelNamesFor(_ context.Context, postings index.Postings) ([]string, error) {
 	namesMap := make(map[string]bool)
-	for _, id := range ids {
-		m.series[id].l.Range(func(lbl labels.Label) {
+	for postings.Next() {
+		m.series[postings.At()].l.Range(func(lbl labels.Label) {
 			namesMap[lbl.Name] = true
 		})
 	}
+	if err := postings.Err(); err != nil {
+		return nil, err
+	}
 	names := make([]string, 0, len(namesMap))
 	for name := range namesMap {
 		names = append(names, name)
@@ -3232,7 +3235,7 @@ func (m mockMatcherIndex) LabelValueFor(context.Context, storage.SeriesRef, stri
 	return "", errors.New("label value for called")
 }
 
-func (m mockMatcherIndex) LabelNamesFor(ctx context.Context, ids ...storage.SeriesRef) ([]string, error) {
+func (m mockMatcherIndex) LabelNamesFor(ctx context.Context, postings index.Postings) ([]string, error) {
 	return nil, errors.New("label names for for called")
 }
 
@@ -3693,7 +3696,7 @@ func (m mockReaderOfLabels) LabelNames(context.Context, ...*labels.Matcher) ([]s
 	panic("LabelNames called")
 }
 
-func (m mockReaderOfLabels) LabelNamesFor(context.Context, ...storage.SeriesRef) ([]string, error) {
+func (m mockReaderOfLabels) LabelNamesFor(context.Context, index.Postings) ([]string, error) {
 	panic("LabelNamesFor called")
 }