From 8f05cd8f9ed90795a189b7aa6874a2db0eb5c96b Mon Sep 17 00:00:00 2001
From: Ben Ye <yb532204897@gmail.com>
Date: Wed, 5 May 2021 13:51:16 -0400
Subject: [PATCH] tsdb: move exemplar series labels to index entry (#8783)

Signed-off-by: yeya24 <yb532204897@gmail.com>
---
 tsdb/exemplar.go      | 21 +++++++++++----------
 tsdb/exemplar_test.go |  4 ++--
 2 files changed, 13 insertions(+), 12 deletions(-)

diff --git a/tsdb/exemplar.go b/tsdb/exemplar.go
index 8eb34a4c6..a7d3182ac 100644
--- a/tsdb/exemplar.go
+++ b/tsdb/exemplar.go
@@ -41,14 +41,15 @@ type CircularExemplarStorage struct {
 }
 
 type indexEntry struct {
-	oldest int
-	newest int
+	oldest       int
+	newest       int
+	seriesLabels labels.Labels
 }
 
 type circularBufferEntry struct {
-	exemplar     exemplar.Exemplar
-	seriesLabels labels.Labels
-	next         int
+	exemplar exemplar.Exemplar
+	next     int
+	ref      *indexEntry
 }
 
 // NewCircularExemplarStorage creates an circular in memory exemplar storage.
@@ -124,10 +125,10 @@ func (ce *CircularExemplarStorage) Select(start, end int64, matchers ...[]*label
 		if e.exemplar.Ts > end || ce.exemplars[idx.newest].exemplar.Ts < start {
 			continue
 		}
-		if !matchesSomeMatcherSet(e.seriesLabels, matchers) {
+		if !matchesSomeMatcherSet(idx.seriesLabels, matchers) {
 			continue
 		}
-		se.SeriesLabels = e.seriesLabels
+		se.SeriesLabels = idx.seriesLabels
 
 		// Loop through all exemplars in the circular buffer for the current series.
 		for e.exemplar.Ts <= end {
@@ -174,7 +175,7 @@ func (ce *CircularExemplarStorage) AddExemplar(l labels.Labels, e exemplar.Exemp
 
 	idx, ok := ce.index[seriesLabels]
 	if !ok {
-		ce.index[seriesLabels] = &indexEntry{oldest: ce.nextIndex}
+		ce.index[seriesLabels] = &indexEntry{oldest: ce.nextIndex, seriesLabels: l}
 	} else {
 		// Check for duplicate vs last stored exemplar for this series.
 		// NB these are expected, add appending them is a no-op.
@@ -195,7 +196,7 @@ func (ce *CircularExemplarStorage) AddExemplar(l labels.Labels, e exemplar.Exemp
 	} else {
 		// There exists exemplar already on this ce.nextIndex entry, drop it, to make place
 		// for others.
-		prevLabels := prev.seriesLabels.String()
+		prevLabels := prev.ref.seriesLabels.String()
 		if prev.next == -1 {
 			// Last item for this series, remove index entry.
 			delete(ce.index, prevLabels)
@@ -208,7 +209,7 @@ func (ce *CircularExemplarStorage) AddExemplar(l labels.Labels, e exemplar.Exemp
 	// since this is the first exemplar stored for this series.
 	ce.exemplars[ce.nextIndex].exemplar = e
 	ce.exemplars[ce.nextIndex].next = -1
-	ce.exemplars[ce.nextIndex].seriesLabels = l
+	ce.exemplars[ce.nextIndex].ref = ce.index[seriesLabels]
 	ce.index[seriesLabels].newest = ce.nextIndex
 
 	ce.nextIndex = (ce.nextIndex + 1) % len(ce.exemplars)
diff --git a/tsdb/exemplar_test.go b/tsdb/exemplar_test.go
index 76976f8be..1c1780d22 100644
--- a/tsdb/exemplar_test.go
+++ b/tsdb/exemplar_test.go
@@ -304,11 +304,11 @@ func TestIndexOverwrite(t *testing.T) {
 	// index entry for series l1 since we just wrote two exemplars for series l2.
 	_, ok := es.index[l1.String()]
 	require.False(t, ok)
-	require.Equal(t, &indexEntry{1, 0}, es.index[l2.String()])
+	require.Equal(t, &indexEntry{1, 0, l2}, es.index[l2.String()])
 
 	err = es.AddExemplar(l1, exemplar.Exemplar{Value: 4, Ts: 4})
 	require.NoError(t, err)
 
 	i := es.index[l2.String()]
-	require.Equal(t, &indexEntry{0, 0}, i)
+	require.Equal(t, &indexEntry{0, 0, l2}, i)
 }