From 19ca93d5cebadd814982f371c70f9e5a4b8a80ca Mon Sep 17 00:00:00 2001
From: Todd Treece <360020+toddtreece@users.noreply.github.com>
Date: Wed, 11 Jan 2023 08:27:47 -0500
Subject: [PATCH] Prometheus: Fix concurrency issue with exemplar sampler
 initialization (#61281)

---
 pkg/tsdb/prometheus/querydata/request.go  | 6 +++---
 pkg/tsdb/prometheus/querydata/response.go | 8 ++++----
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/pkg/tsdb/prometheus/querydata/request.go b/pkg/tsdb/prometheus/querydata/request.go
index 99acce2a2a2..e8175e84be4 100644
--- a/pkg/tsdb/prometheus/querydata/request.go
+++ b/pkg/tsdb/prometheus/querydata/request.go
@@ -43,7 +43,7 @@ type QueryData struct {
 	URL                string
 	TimeInterval       string
 	enableWideSeries   bool
-	exemplarSampler    exemplar.Sampler
+	exemplarSampler    func() exemplar.Sampler
 }
 
 func New(
@@ -67,10 +67,10 @@ func New(
 	promClient := client.NewClient(httpClient, httpMethod, settings.URL)
 
 	// standard deviation sampler is the default for backwards compatibility
-	exemplarSampler := exemplar.NewStandardDeviationSampler()
+	exemplarSampler := exemplar.NewStandardDeviationSampler
 
 	if features.IsEnabled(featuremgmt.FlagDisablePrometheusExemplarSampling) {
-		exemplarSampler = exemplar.NewNoOpSampler()
+		exemplarSampler = exemplar.NewNoOpSampler
 	}
 
 	return &QueryData{
diff --git a/pkg/tsdb/prometheus/querydata/response.go b/pkg/tsdb/prometheus/querydata/response.go
index 2d8f8a2a06f..b0ab2049d82 100644
--- a/pkg/tsdb/prometheus/querydata/response.go
+++ b/pkg/tsdb/prometheus/querydata/response.go
@@ -47,14 +47,14 @@ func (s *QueryData) parseResponse(ctx context.Context, q *models.Query, res *htt
 }
 
 func (s *QueryData) processExemplars(q *models.Query, dr *backend.DataResponse) *backend.DataResponse {
-	s.exemplarSampler.Reset()
+	sampler := s.exemplarSampler()
 	labelTracker := exemplar.NewLabelTracker()
 
 	// we are moving from a multi-frame response returned
 	// by the converter to a single exemplar frame,
 	// so we need to build a new frame array with the
 	// old exemplar frames filtered out
-	framer := exemplar.NewFramer(s.exemplarSampler, labelTracker)
+	framer := exemplar.NewFramer(sampler, labelTracker)
 
 	for _, frame := range dr.Frames {
 		// we don't need to process non-exemplar frames
@@ -69,7 +69,7 @@ func (s *QueryData) processExemplars(q *models.Query, dr *backend.DataResponse)
 		framer.SetRefID(frame.RefID)
 
 		step := time.Duration(frame.Fields[0].Config.Interval) * time.Millisecond
-		s.exemplarSampler.SetStep(step)
+		sampler.SetStep(step)
 
 		seriesLabels := getSeriesLabels(frame)
 		labelTracker.Add(seriesLabels)
@@ -83,7 +83,7 @@ func (s *QueryData) processExemplars(q *models.Query, dr *backend.DataResponse)
 				Timestamp:    row[0].(time.Time),
 				SeriesLabels: seriesLabels,
 			}
-			s.exemplarSampler.Add(ex)
+			sampler.Add(ex)
 		}
 	}