Properly initialize head time

This fixes various issues when initializing the head time range
under different starting conditions.

Signed-off-by: Fabian Reinartz <freinartz@google.com>

db_test.go

@@ -19,6 +19,7 @@ import (
 	"math"
 	"math/rand"
 	"os"
+	"path"
 	"path/filepath"
 	"sort"
 	"testing"
@@ -30,6 +31,7 @@ import (
 	"github.com/prometheus/tsdb/index"
 	"github.com/prometheus/tsdb/labels"
 	"github.com/prometheus/tsdb/testutil"
+	"github.com/prometheus/tsdb/wal"
 )
 
 func openTestDB(t testing.TB, opts *Options) (db *DB, close func()) {
@@ -1193,3 +1195,109 @@ func TestQuerierWithBoundaryChunks(t *testing.T) {
 	count := len(q.(*querier).blocks)
 	testutil.Assert(t, count == 2, "expected 2 blocks in querier, got %d", count)
 }
+
+func TestInitializeHeadTimestamp(t *testing.T) {
+	t.Run("clean", func(t *testing.T) {
+		dir, err := ioutil.TempDir("", "test_head_init")
+		testutil.Ok(t, err)
+		defer os.RemoveAll(dir)
+
+		db, err := Open(dir, nil, nil, nil)
+		testutil.Ok(t, err)
+
+		// Should be set to init values if no WAL or blocks exist so far.
+		testutil.Equals(t, int64(math.MaxInt64), db.head.MinTime())
+		testutil.Equals(t, int64(math.MinInt64), db.head.MaxTime())
+
+		// First added sample initializes the writable range.
+		app := db.Appender()
+		_, err = app.Add(labels.FromStrings("a", "b"), 1000, 1)
+		testutil.Ok(t, err)
+
+		testutil.Equals(t, int64(1000), db.head.MinTime())
+		testutil.Equals(t, int64(1000), db.head.MaxTime())
+	})
+	t.Run("wal-only", func(t *testing.T) {
+		dir, err := ioutil.TempDir("", "test_head_init")
+		testutil.Ok(t, err)
+		defer os.RemoveAll(dir)
+
+		testutil.Ok(t, os.MkdirAll(path.Join(dir, "wal"), 0777))
+		w, err := wal.New(nil, nil, path.Join(dir, "wal"))
+		testutil.Ok(t, err)
+
+		var enc RecordEncoder
+		err = w.Log(
+			enc.Series([]RefSeries{
+				{Ref: 123, Labels: labels.FromStrings("a", "1")},
+				{Ref: 124, Labels: labels.FromStrings("a", "2")},
+			}, nil),
+			enc.Samples([]RefSample{
+				{Ref: 123, T: 5000, V: 1},
+				{Ref: 124, T: 15000, V: 1},
+			}, nil),
+		)
+		testutil.Ok(t, err)
+		testutil.Ok(t, w.Close())
+
+		db, err := Open(dir, nil, nil, nil)
+		testutil.Ok(t, err)
+
+		testutil.Equals(t, int64(5000), db.head.MinTime())
+		testutil.Equals(t, int64(15000), db.head.MaxTime())
+	})
+	t.Run("existing-block", func(t *testing.T) {
+		dir, err := ioutil.TempDir("", "test_head_init")
+		testutil.Ok(t, err)
+		defer os.RemoveAll(dir)
+
+		id := ulid.MustNew(2000, nil)
+		createEmptyBlock(t, path.Join(dir, id.String()), &BlockMeta{
+			ULID:    id,
+			MinTime: 1000,
+			MaxTime: 2000,
+		})
+
+		db, err := Open(dir, nil, nil, nil)
+		testutil.Ok(t, err)
+
+		testutil.Equals(t, int64(2000), db.head.MinTime())
+		testutil.Equals(t, int64(2000), db.head.MaxTime())
+	})
+	t.Run("existing-block-and-wal", func(t *testing.T) {
+		dir, err := ioutil.TempDir("", "test_head_init")
+		testutil.Ok(t, err)
+		defer os.RemoveAll(dir)
+
+		id := ulid.MustNew(2000, nil)
+		createEmptyBlock(t, path.Join(dir, id.String()), &BlockMeta{
+			ULID:    id,
+			MinTime: 1000,
+			MaxTime: 6000,
+		})
+
+		testutil.Ok(t, os.MkdirAll(path.Join(dir, "wal"), 0777))
+		w, err := wal.New(nil, nil, path.Join(dir, "wal"))
+		testutil.Ok(t, err)
+
+		var enc RecordEncoder
+		err = w.Log(
+			enc.Series([]RefSeries{
+				{Ref: 123, Labels: labels.FromStrings("a", "1")},
+				{Ref: 124, Labels: labels.FromStrings("a", "2")},
+			}, nil),
+			enc.Samples([]RefSample{
+				{Ref: 123, T: 5000, V: 1},
+				{Ref: 124, T: 15000, V: 1},
+			}, nil),
+		)
+		testutil.Ok(t, err)
+		testutil.Ok(t, w.Close())
+
+		db, err := Open(dir, nil, nil, nil)
+		testutil.Ok(t, err)
+
+		testutil.Equals(t, int64(6000), db.head.MinTime())
+		testutil.Equals(t, int64(15000), db.head.MaxTime())
+	})
+}

head.go

@@ -183,7 +183,7 @@ func NewHead(r prometheus.Registerer, l log.Logger, wal *wal.WAL, chunkRange int
 		wal:        wal,
 		logger:     l,
 		chunkRange: chunkRange,
-		minTime:    math.MinInt64,
+		minTime:    math.MaxInt64,
 		maxTime:    math.MinInt64,
 		series:     newStripeSeries(),
 		values:     map[string]stringset{},
@@ -200,17 +200,17 @@ func NewHead(r prometheus.Registerer, l log.Logger, wal *wal.WAL, chunkRange int
 // them on to other workers.
 // Samples before the mint timestamp are discarded.
 func (h *Head) processWALSamples(
-	mint int64,
+	minValidTime int64,
 	partition, total uint64,
 	input <-chan []RefSample, output chan<- []RefSample,
 ) (unknownRefs uint64) {
 	defer close(output)
 
-	maxt := h.MaxTime()
+	mint, maxt := int64(math.MaxInt64), int64(math.MinInt64)
 
 	for samples := range input {
 		for _, s := range samples {
-			if s.T < mint || s.Ref%total != partition {
+			if s.T < minValidTime || s.Ref%total != partition {
 				continue
 			}
 			ms := h.series.getByID(s.Ref)
@@ -226,10 +226,27 @@ func (h *Head) processWALSamples(
 			if s.T > maxt {
 				maxt = s.T
 			}
+			if s.T < mint {
+				mint = s.T
+			}
 		}
 		output <- samples
 	}
+	h.updateMinMaxTime(mint, maxt)
 
+	return unknownRefs
+}
+
+func (h *Head) updateMinMaxTime(mint, maxt int64) {
+	for {
+		lt := h.MinTime()
+		if mint >= lt {
+			break
+		}
+		if atomic.CompareAndSwapInt64(&h.minTime, lt, mint) {
+			break
+		}
+	}
 	for {
 		ht := h.MaxTime()
 		if maxt <= ht {
@@ -239,12 +256,15 @@ func (h *Head) processWALSamples(
 			break
 		}
 	}
-
-	return unknownRefs
 }
 
 func (h *Head) loadWAL(r *wal.Reader) error {
-	mint := h.MinTime()
+	minValidTime := h.MinTime()
+	// If the min time is still uninitialized (no persisted blocks yet),
+	// we accept all sample timestamps from the WAL.
+	if minValidTime == math.MaxInt64 {
+		minValidTime = math.MinInt64
+	}
 
 	// Track number of samples that referenced a series we don't know about
 	// for error reporting.
@@ -265,7 +285,7 @@ func (h *Head) loadWAL(r *wal.Reader) error {
 		output := make(chan []RefSample, 300)
 
 		go func(i int, input <-chan []RefSample, output chan<- []RefSample) {
-			unknown := h.processWALSamples(mint, uint64(i), uint64(n), input, output)
+			unknown := h.processWALSamples(minValidTime, uint64(i), uint64(n), input, output)
 			atomic.AddUint64(&unknownRefs, unknown)
 			wg.Done()
 		}(i, input, output)
@@ -327,7 +347,7 @@ func (h *Head) loadWAL(r *wal.Reader) error {
 			}
 			for _, s := range tstones {
 				for _, itv := range s.intervals {
-					if itv.Maxt < mint {
+					if itv.Maxt < minValidTime {
 						continue
 					}
 					h.tombstones.addInterval(s.ref, itv)
@@ -400,9 +420,9 @@ func (h *Head) Init() error {
 
 // Truncate removes old data before mint from the head.
 func (h *Head) Truncate(mint int64) error {
-	initialize := h.MinTime() == math.MinInt64
+	initialize := h.MinTime() == math.MaxInt64
 
-	if h.MinTime() >= mint {
+	if h.MinTime() >= mint && !initialize {
 		return nil
 	}
 	atomic.StoreInt64(&h.minTime, mint)
@@ -462,10 +482,7 @@ func (h *Head) Truncate(mint int64) error {
 // for a compltely fresh head with an empty WAL.
 // Returns true if the initialization took an effect.
 func (h *Head) initTime(t int64) (initialized bool) {
-	// In the init state, the head has a high timestamp of math.MinInt64.
+	if !atomic.CompareAndSwapInt64(&h.minTime, math.MaxInt64, t) {
-	mint, _ := rangeForTimestamp(t, h.chunkRange)
-
-	if !atomic.CompareAndSwapInt64(&h.minTime, math.MinInt64, mint) {
 		return false
 	}
 	// Ensure that max time is initialized to at least the min time we just set.
@@ -536,7 +553,7 @@ func (h *Head) Appender() Appender {
 
 	// The head cache might not have a starting point yet. The init appender
 	// picks up the first appended timestamp as the base.
-	if h.MinTime() == math.MinInt64 {
+	if h.MinTime() == math.MaxInt64 {
 		return &initAppender{head: h}
 	}
 	return h.appender()
@@ -544,10 +561,11 @@ func (h *Head) Appender() Appender {
 
 func (h *Head) appender() *headAppender {
 	return &headAppender{
-		head:    h,
+		head:         h,
-		mint:    h.MaxTime() - h.chunkRange/2,
+		minValidTime: h.MaxTime() - h.chunkRange/2,
-		maxt:    math.MinInt64,
+		mint:         math.MaxInt64,
-		samples: h.getAppendBuffer(),
+		maxt:         math.MinInt64,
+		samples:      h.getAppendBuffer(),
 	}
 }
 
@@ -576,15 +594,16 @@ func (h *Head) putBytesBuffer(b []byte) {
 }
 
 type headAppender struct {
-	head       *Head
+	head         *Head
-	mint, maxt int64
+	minValidTime int64 // No samples below this timestamp are allowed.
+	mint, maxt   int64
 
 	series  []RefSeries
 	samples []RefSample
 }
 
 func (a *headAppender) Add(lset labels.Labels, t int64, v float64) (uint64, error) {
-	if t < a.mint {
+	if t < a.minValidTime {
 		return 0, ErrOutOfBounds
 	}
 
@@ -611,9 +630,12 @@ func (a *headAppender) AddFast(ref uint64, t int64, v float64) error {
 	if err != nil {
 		return err
 	}
-	if t < a.mint {
+	if t < a.minValidTime {
 		return ErrOutOfBounds
 	}
+	if t < a.mint {
+		a.mint = t
+	}
 	if t > a.maxt {
 		a.maxt = t
 	}
@@ -682,16 +704,7 @@ func (a *headAppender) Commit() error {
 	}
 
 	a.head.metrics.samplesAppended.Add(float64(total))
-
+	a.head.updateMinMaxTime(a.mint, a.maxt)
-	for {
-		ht := a.head.MaxTime()
-		if a.maxt <= ht {
-			break
-		}
-		if atomic.CompareAndSwapInt64(&a.head.maxTime, ht, a.maxt) {
-			break
-		}
-	}
 
 	return nil
 }