From bc1d7d7f270bf0c4553d3a972bcba72a3acf712a Mon Sep 17 00:00:00 2001
From: Marco Pracucci <marco@pracucci.com>
Date: Mon, 8 Jun 2020 20:55:53 +0200
Subject: [PATCH 1/2] Fixed incorrect query results caused by buffer reuse in
 merge adapter (#7361)

Signed-off-by: Marco Pracucci <marco@pracucci.com>
---
 storage/fanout_test.go | 15 +++++++++++----
 storage/generic.go     | 14 ++++++--------
 2 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/storage/fanout_test.go b/storage/fanout_test.go
index cc839b6ed..a5d04ea8f 100644
--- a/storage/fanout_test.go
+++ b/storage/fanout_test.go
@@ -195,10 +195,18 @@ func TestMergeQuerierWithChainMerger(t *testing.T) {
 			}
 			qs = append(qs, tc.extraQueriers...)
 
-			merged, _, _ := NewMergeQuerier(qs[0], qs, ChainedSeriesMerge).Select(false, nil)
-			for merged.Next() {
+			mergedQuerier, _, _ := NewMergeQuerier(qs[0], qs, ChainedSeriesMerge).Select(false, nil)
+
+			// Get all merged series upfront to make sure there are no incorrectly retained shared
+			// buffers causing bugs.
+			var mergedSeries []Series
+			for mergedQuerier.Next() {
+				mergedSeries = append(mergedSeries, mergedQuerier.At())
+			}
+			testutil.Ok(t, mergedQuerier.Err())
+
+			for _, actualSeries := range mergedSeries {
 				testutil.Assert(t, tc.expected.Next(), "Expected Next() to be true")
-				actualSeries := merged.At()
 				expectedSeries := tc.expected.At()
 				testutil.Equals(t, expectedSeries.Labels(), actualSeries.Labels())
 
@@ -207,7 +215,6 @@ func TestMergeQuerierWithChainMerger(t *testing.T) {
 				testutil.Equals(t, expErr, actErr)
 				testutil.Equals(t, expSmpl, actSmpl)
 			}
-			testutil.Ok(t, merged.Err())
 			testutil.Assert(t, !tc.expected.Next(), "Expected Next() to be false")
 		})
 	}
diff --git a/storage/generic.go b/storage/generic.go
index a5a694cb2..d23e51a6c 100644
--- a/storage/generic.go
+++ b/storage/generic.go
@@ -108,26 +108,24 @@ func (q *chunkQuerierAdapter) Select(sortSeries bool, hints *SelectHints, matche
 
 type seriesMergerAdapter struct {
 	VerticalSeriesMergeFunc
-	buf []Series
 }
 
 func (a *seriesMergerAdapter) Merge(s ...Labels) Labels {
-	a.buf = a.buf[:0]
+	buf := make([]Series, 0, len(s))
 	for _, ser := range s {
-		a.buf = append(a.buf, ser.(Series))
+		buf = append(buf, ser.(Series))
 	}
-	return a.VerticalSeriesMergeFunc(a.buf...)
+	return a.VerticalSeriesMergeFunc(buf...)
 }
 
 type chunkSeriesMergerAdapter struct {
 	VerticalChunkSeriesMergerFunc
-	buf []ChunkSeries
 }
 
 func (a *chunkSeriesMergerAdapter) Merge(s ...Labels) Labels {
-	a.buf = a.buf[:0]
+	buf := make([]ChunkSeries, 0, len(s))
 	for _, ser := range s {
-		a.buf = append(a.buf, ser.(ChunkSeries))
+		buf = append(buf, ser.(ChunkSeries))
 	}
-	return a.VerticalChunkSeriesMergerFunc(a.buf...)
+	return a.VerticalChunkSeriesMergerFunc(buf...)
 }

From 0f34535009dfae68ed68d5ee8a27e0f9b666c9ac Mon Sep 17 00:00:00 2001
From: Bartlomiej Plotka <bwplotka@gmail.com>
Date: Tue, 9 Jun 2020 05:47:53 +0100
Subject: [PATCH 2/2] Cut 2.18.2 + cherry pick of query bugfix.

Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
---
 CHANGELOG.md | 4 ++++
 VERSION      | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index aec464e7f..623fa8f73 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 2.18.2 / 2020-06-09
+
+* [BUGFIX] TSDB: Fix incorrect query results when using Prometheus with remote reads configured #7361
+
 ## 2.18.1 / 2020-05-07
 
 * [BUGFIX] TSDB: Fixed snapshot API. #7217
diff --git a/VERSION b/VERSION
index a36e9b090..61dc3342f 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.18.1
+2.18.2