fix: avoid copying label values from tsdb unless required (#17077)

pkg/storage/stores/shipper/indexshipper/tsdb/head_read.go

@@ -55,18 +55,6 @@ func (h *headIndexReader) Symbols() index.StringIter {
 	return h.head.postings.Symbols()
 }
 
-// SortedLabelValues returns label values present in the head for the
-// specific label name that are within the time range mint to maxt.
-// If matchers are specified the returned result set is reduced
-// to label values of metrics matching the matchers.
-func (h *headIndexReader) SortedLabelValues(name string, matchers ...*labels.Matcher) ([]string, error) {
-	values, err := h.LabelValues(name, matchers...)
-	if err == nil {
-		sort.Strings(values)
-	}
-	return values, err
-}
-
 // LabelValues returns label values present in the head for the
 // specific label name that are within the time range mint to maxt.
 // If matchers are specified the returned result set is reduced

pkg/storage/stores/shipper/indexshipper/tsdb/index/index.go

@@ -1617,16 +1617,8 @@ func (r *Reader) SymbolTableSize() uint64 {
 	return uint64(r.symbols.Size())
 }
 
-// SortedLabelValues returns value tuples that exist for the given label name.
-func (r *Reader) SortedLabelValues(name string, matchers ...*labels.Matcher) ([]string, error) {
-	values, err := r.LabelValues(name, matchers...)
-	if err == nil && r.version == FormatV1 {
-		sort.Strings(values)
-	}
-	return values, err
-}
-
 // LabelValues returns value tuples that exist for the given label name.
+// The returned values should be copied if they need to be used beyond the current tsdb read operation, including sending back as response.
 // TODO(replay): Support filtering by matchers
 func (r *Reader) LabelValues(name string, matchers ...*labels.Matcher) ([]string, error) {
 	if len(matchers) > 0 {
@@ -1670,7 +1662,7 @@ func (r *Reader) LabelValues(name string, matchers ...*labels.Matcher) ([]string
 		} else {
 			d.Skip(skip)
 		}
-		s := string(d.UvarintBytes()) // Label value.
+		s := yoloString(d.UvarintBytes()) // Label value.
 		values = append(values, s)
 		if s == lastVal {
 			break

pkg/storage/stores/shipper/indexshipper/tsdb/index/index_test.go

@@ -449,9 +449,10 @@ func TestPersistence_index_e2e(t *testing.T) {
 	for k, v := range labelPairs {
 		sort.Strings(v)
 
-		res, err := ir.SortedLabelValues(k)
+		res, err := ir.LabelValues(k)
 		require.NoError(t, err)
 
+		sort.Strings(res)
 		require.Equal(t, len(v), len(res))
 		for i := 0; i < len(v); i++ {
 			require.Equal(t, v[i], res[i])

pkg/storage/stores/shipper/indexshipper/tsdb/querier.go

@@ -51,9 +51,6 @@ type IndexReader interface {
 	// beyond the lifetime of the index reader.
 	Symbols() index.StringIter
 
-	// SortedLabelValues returns sorted possible label values.
-	SortedLabelValues(name string, matchers ...*labels.Matcher) ([]string, error)
-
 	// LabelValues returns possible label values which may not be sorted.
 	LabelValues(name string, matchers ...*labels.Matcher) ([]string, error)
 

pkg/storage/stores/shipper/indexshipper/tsdb/single_file_index.go

@@ -7,6 +7,7 @@ import (
 	"io"
 	"math"
 	"path/filepath"
+	"strings"
 	"time"
 
 	"github.com/opentracing/opentracing-go"
@@ -268,10 +269,17 @@ func (i *TSDBIndex) LabelNames(_ context.Context, _ string, _, _ model.Time, mat
 }
 
 func (i *TSDBIndex) LabelValues(_ context.Context, _ string, _, _ model.Time, name string, matchers ...*labels.Matcher) ([]string, error) {
-	if len(matchers) == 0 {
-		return i.reader.LabelValues(name)
+	if len(matchers) != 0 {
+		return labelValuesWithMatchers(i.reader, name, matchers...)
+	}
+
+	labelValues, err := i.reader.LabelValues(name)
+	if err != nil {
+		return nil, err
 	}
-	return labelValuesWithMatchers(i.reader, name, matchers...)
+
+	// cloning the string
+	return cloneStringList(labelValues), nil
 }
 
 func (i *TSDBIndex) Checksum() uint32 {
@@ -454,3 +462,11 @@ func (i *TSDBIndex) Volume(
 		return p.Err()
 	})
 }
+
+func cloneStringList(strs []string) []string {
+	res := make([]string, 0, len(strs))
+	for _, str := range strs {
+		res = append(res, strings.Clone(str))
+	}
+	return res
+}