From 56b3a015b6864af3d9b4063f0807ddbc06fa46fc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Gy=C3=B6rgy=20Krajcsovits?= <gyorgy.krajcsovits@grafana.com>
Date: Wed, 20 Sep 2023 14:32:20 +0200
Subject: [PATCH] Add regression test for duplicate detection at chunk size
 limit
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TestHeadDetectsDuplcateSampleAtSizeLimit tests a regression where a
 duplicate sample,is appended to the head, right when the head chunk is
 at the size limit. The test adds all samples as duplicate, thus
 expecting that the result has exactly half of the samples.

Signed-off-by: György Krajcsovits <gyorgy.krajcsovits@grafana.com>
---
 tsdb/head_test.go | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/tsdb/head_test.go b/tsdb/head_test.go
index 2aa97cd440..3d271e93bb 100644
--- a/tsdb/head_test.go
+++ b/tsdb/head_test.go
@@ -5499,3 +5499,49 @@ func TestCuttingNewHeadChunks(t *testing.T) {
 		})
 	}
 }
+
+// TestHeadDetectsDuplcateSampleAtSizeLimit tests a regression where a duplicate sample
+// is appended to the head, right when the head chunk is at the size limit.
+// The test adds all samples as duplicate, thus expecting that the result has
+// exactly half of the samples.
+func TestHeadDetectsDuplicateSampleAtSizeLimit(t *testing.T) {
+	numSamples := 1000
+	baseTS := int64(1695209650)
+
+	h, _ := newTestHead(t, DefaultBlockDuration, wlog.CompressionNone, false)
+	defer func() {
+		require.NoError(t, h.Close())
+	}()
+
+	a := h.Appender(context.Background())
+	var err error
+	vals := []float64{math.MaxFloat64, 0x00} // Use the worst case scenario for the XOR encoding. Otherwise we hit the sample limit before the size limit.
+	for i := 0; i < numSamples; i++ {
+		ts := baseTS + int64(i/2)*10000
+		a.Append(0, labels.FromStrings("foo", "bar"), ts, vals[(i/2)%len(vals)])
+		err = a.Commit()
+		require.NoError(t, err)
+		a = h.Appender(context.Background())
+	}
+
+	indexReader, err := h.Index()
+	require.NoError(t, err)
+
+	var (
+		chunks  []chunks.Meta
+		builder labels.ScratchBuilder
+	)
+	require.NoError(t, indexReader.Series(1, &builder, &chunks))
+
+	chunkReader, err := h.Chunks()
+	require.NoError(t, err)
+
+	storedSampleCount := 0
+	for _, chunkMeta := range chunks {
+		chunk, err := chunkReader.Chunk(chunkMeta)
+		require.NoError(t, err)
+		storedSampleCount += chunk.NumSamples()
+	}
+
+	require.Equal(t, numSamples/2, storedSampleCount)
+}