Fix ToEncodedChunks minT for recoded chunks

There was a bug where the min time of a chunk was adjusted even
if it was only recoded and not completely new.

Signed-off-by: György Krajcsovits <gyorgy.krajcsovits@grafana.com>

tsdb/ooo_head.go

@@ -144,9 +144,9 @@ func (o *OOOChunk) ToEncodedChunks(mint, maxt int64) (chks []memChunk, err error
 			if newChunk != nil { // A new chunk was allocated.
 				if !recoded {
 					chks = append(chks, memChunk{chunk, cmint, cmaxt, nil})
+					cmint = s.t
 				}
 				chunk = newChunk
-				cmint = s.t
 			}
 		case chunkenc.EncFloatHistogram:
 			// Ignoring ok is ok, since we don't want to compare to the wrong previous appender anyway.
@@ -159,9 +159,9 @@ func (o *OOOChunk) ToEncodedChunks(mint, maxt int64) (chks []memChunk, err error
 			if newChunk != nil { // A new chunk was allocated.
 				if !recoded {
 					chks = append(chks, memChunk{chunk, cmint, cmaxt, nil})
+					cmint = s.t
 				}
 				chunk = newChunk
-				cmint = s.t
 			}
 		}
 		cmaxt = s.t

tsdb/ooo_head_test.go

@@ -14,8 +14,12 @@
 package tsdb
 
 import (
+	"math"
 	"testing"
 
+	"github.com/prometheus/prometheus/model/histogram"
+	"github.com/prometheus/prometheus/storage"
+	"github.com/prometheus/prometheus/tsdb/chunkenc"
 	"github.com/prometheus/prometheus/tsdb/tsdbutil"
 
 	"github.com/stretchr/testify/require"
@@ -145,3 +149,100 @@ func testOOOInsertDuplicate(t *testing.T,
 		}
 	}
 }
+
+type chunkVerify struct {
+	encoding chunkenc.Encoding
+	minTime  int64
+	maxTime  int64
+}
+
+func TestOOOChunks_ToEncodedChunks(t *testing.T) {
+	h1 := tsdbutil.GenerateTestHistogram(1)
+	// Make h2 appendible but with more buckets, to trigger recoding.
+	h2 := h1.Copy()
+	h2.PositiveSpans = append(h2.PositiveSpans, histogram.Span{Offset: 1, Length: 1})
+	h2.PositiveBuckets = append(h2.PositiveBuckets, 12)
+
+	testCases := map[string]struct {
+		samples               []sample
+		expectedCounterResets []histogram.CounterResetHint
+		expectedChunks        []chunkVerify
+	}{
+		"empty": {
+			samples: []sample{},
+		},
+		"has a recoded histogram": { // Regression test for wrong minT, maxT in histogram recoding.
+			samples: []sample{
+				{t: 0, h: h1},
+				{t: 1, h: h2},
+			},
+			expectedCounterResets: []histogram.CounterResetHint{histogram.UnknownCounterReset, histogram.NotCounterReset},
+			expectedChunks: []chunkVerify{
+				{encoding: chunkenc.EncHistogram, minTime: 0, maxTime: 1},
+			},
+		},
+	}
+
+	for name, tc := range testCases {
+		t.Run(name, func(t *testing.T) {
+			// Sanity check.
+			require.Equal(t, len(tc.samples), len(tc.expectedCounterResets), "number of samples and counter resets")
+
+			oooChunk := OOOChunk{}
+			for _, s := range tc.samples {
+				switch s.Type() {
+				case chunkenc.ValFloat:
+					oooChunk.Insert(s.t, s.f, nil, nil)
+				case chunkenc.ValHistogram:
+					oooChunk.Insert(s.t, 0, s.h.Copy(), nil)
+				case chunkenc.ValFloatHistogram:
+					oooChunk.Insert(s.t, 0, nil, s.fh.Copy())
+				default:
+					t.Fatalf("unexpected sample type %d", s.Type())
+				}
+			}
+
+			chunks, err := oooChunk.ToEncodedChunks(math.MinInt64, math.MaxInt64)
+			require.NoError(t, err)
+			require.Equal(t, len(tc.expectedChunks), len(chunks), "number of chunks")
+			sampleIndex := 0
+			for i, c := range chunks {
+				require.Equal(t, tc.expectedChunks[i].encoding, c.chunk.Encoding(), "chunk %d encoding", i)
+				require.Equal(t, tc.expectedChunks[i].minTime, c.minTime, "chunk %d minTime", i)
+				require.Equal(t, tc.expectedChunks[i].maxTime, c.maxTime, "chunk %d maxTime", i)
+				samples, err := storage.ExpandSamples(c.chunk.Iterator(nil), newSample)
+				require.GreaterOrEqual(t, len(tc.samples)-sampleIndex, len(samples), "too many samples in chunk %d expected less than %d", i, len(tc.samples)-sampleIndex)
+				require.NoError(t, err)
+				if len(samples) == 0 {
+					// Ignore empty chunks.
+					continue
+				}
+				switch c.chunk.Encoding() {
+				case chunkenc.EncXOR:
+					for j, s := range samples {
+						require.Equal(t, chunkenc.ValFloat, s.Type())
+						require.Equal(t, tc.samples[sampleIndex+j].f, s.F(), "sample %d", sampleIndex+j)
+					}
+				case chunkenc.EncHistogram:
+					for j, s := range samples {
+						require.Equal(t, chunkenc.ValHistogram, s.Type())
+						require.Equal(t, tc.expectedCounterResets[sampleIndex+j], s.H().CounterResetHint, "sample reset hint %d", sampleIndex+j)
+						compareTo := tc.samples[sampleIndex+j].h.Copy()
+						compareTo.CounterResetHint = tc.expectedCounterResets[sampleIndex+j]
+						require.Equal(t, compareTo, s.H().Compact(0), "sample %d", sampleIndex+j)
+					}
+				case chunkenc.EncFloatHistogram:
+					for j, s := range samples {
+						require.Equal(t, chunkenc.ValFloatHistogram, s.Type())
+						require.Equal(t, tc.expectedCounterResets[sampleIndex+j], s.FH().CounterResetHint, "sample reset hint %d", sampleIndex+j)
+						compareTo := tc.samples[sampleIndex+j].fh.Copy()
+						compareTo.CounterResetHint = tc.expectedCounterResets[sampleIndex+j]
+						require.Equal(t, compareTo, s.FH().Compact(0), "sample %d", sampleIndex+j)
+					}
+				}
+				sampleIndex += len(samples)
+			}
+			require.Equal(t, len(tc.samples), sampleIndex, "number of samples")
+		})
+	}
+}