initial step

Signed-off-by: Vanshikav123 <vanshikav928@gmail.com>

storage/remote/read.go

@@ -18,7 +18,9 @@ import (
 	"errors"
 	"fmt"
 
+	"github.com/prometheus/prometheus/model/exemplar"
 	"github.com/prometheus/prometheus/model/labels"
+	"github.com/prometheus/prometheus/prompb"
 	"github.com/prometheus/prometheus/storage"
 	"github.com/prometheus/prometheus/util/annotations"
 )
@@ -130,6 +132,7 @@ type querier struct {
 	// Derived from configuration.
 	externalLabels    labels.Labels
 	requiredMatchers  []*labels.Matcher
+	exemplarQueryable storage.ExemplarQueryable
 }
 
 // Select implements storage.Querier and uses the given matchers to read series sets from the client.
@@ -165,10 +168,23 @@ func (q *querier) Select(ctx context.Context, sortSeries bool, hints *storage.Se
 		return storage.ErrSeriesSet(fmt.Errorf("toQuery: %w", err))
 	}
 
+	exemplarQuerier, err := q.exemplarQueryable.ExemplarQuerier(ctx)
+	if err != nil {
+		return storage.ErrSeriesSet(fmt.Errorf("ExemplarQuerier: %w", err))
+	}
+
+	exemplars, err := exemplarQuerier.Select(q.mint, q.maxt, [][]*labels.Matcher{matchers}...)
+	if err != nil {
+		return storage.ErrSeriesSet(fmt.Errorf("exemplar select: %w", err))
+	}
+
 	res, err := q.client.Read(ctx, query, sortSeries)
 	if err != nil {
 		return storage.ErrSeriesSet(fmt.Errorf("remote_read: %w", err))
 	}
+
+	res = mergeSeriesWithExemplars(res, exemplars)
+
 	return newSeriesSetFilter(res, added)
 }
 
@@ -278,3 +294,52 @@ func (sf seriesFilter) Labels() labels.Labels {
 	b.Del(sf.toFilter...)
 	return b.Labels()
 }
+func mergeSeriesWithExemplars(ss storage.SeriesSet, exemplars []exemplar.QueryResult) storage.SeriesSet {
+	exemplarMap := make(map[uint64][]prompb.Exemplar)
+	for _, result := range exemplars {
+
+		key := result.SeriesLabels.Hash()
+		for _, ex := range result.Exemplars {
+
+			if ex.HasTs {
+				exemplarMap[key] = append(exemplarMap[key], prompb.Exemplar{
+					Labels:    prompb.FromLabels(ex.Labels, nil),
+					Value:     ex.Value,
+					Timestamp: ex.Ts,
+				})
+			}
+		}
+	}
+
+	// Wrap the original SeriesSet to inject exemplars into the series.
+	return &seriesSetWithExemplars{
+		SeriesSet:   ss,
+		exemplarMap: exemplarMap,
+	}
+}
+
+type seriesSetWithExemplars struct {
+	storage.SeriesSet
+	exemplarMap map[uint64][]prompb.Exemplar
+}
+
+// At returns a series with exemplars if they exist for the series' labels.
+func (sswe *seriesSetWithExemplars) At() storage.Series {
+	series := sswe.SeriesSet.At()
+	key := series.Labels().Hash()
+	exemplars := sswe.exemplarMap[key]
+
+	return &seriesWithExemplars{
+		Series:    series,
+		exemplars: exemplars,
+	}
+}
+
+type seriesWithExemplars struct {
+	storage.Series
+	exemplars []prompb.Exemplar
+}
+
+func (swe *seriesWithExemplars) Exemplars() []prompb.Exemplar {
+	return swe.exemplars
+}