tsdb: use simpler map key to improve exemplar ingest performance (#10111)

* tsdb: fix exemplar benchmarks

Go benchmarks are expected to do an amount of work that varies with
the `b.N` parameter. Previously these benchmarks would report a result
like 0.01 ns/op, which is nonsense.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

* tsdb: use simpler map key to improve exemplar perf

Prometheus holds an index of exemplars so it can discard the oldest one
for a series when a new one is added.
Since the keys are not for human eyes, we can use a simpler format
and save the effort of quoting label values.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

* Exemplars: allocate index map with estimated size

This avoids Go having to re-size the map several times as it grows.
16 exemplars per series is a guess; if it is too low then the map will
be sparse, while if it is too high then the map will have to resize once
or twice.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

tsdb/exemplar.go

@@ -27,8 +27,12 @@ import (
 	"github.com/prometheus/prometheus/storage"
 )
 
-// Indicates that there is no index entry for an exmplar.
-const noExemplar = -1
+const (
+	// Indicates that there is no index entry for an exmplar.
+	noExemplar = -1
+	// Estimated number of exemplars per series, for sizing the index.
+	estimatedExemplarsPerSeries = 16
+)
 
 type CircularExemplarStorage struct {
 	lock      sync.RWMutex
@@ -117,7 +121,7 @@ func NewCircularExemplarStorage(len int64, m *ExemplarMetrics) (ExemplarStorage,
 	}
 	c := &CircularExemplarStorage{
 		exemplars: make([]*circularBufferEntry, len),
-		index:     make(map[string]*indexEntry),
+		index:     make(map[string]*indexEntry, len/estimatedExemplarsPerSeries),
 		metrics:   m,
 	}
 
@@ -202,7 +206,8 @@ Outer:
 }
 
 func (ce *CircularExemplarStorage) ValidateExemplar(l labels.Labels, e exemplar.Exemplar) error {
-	seriesLabels := l.String()
+	var buf [1024]byte
+	seriesLabels := l.Bytes(buf[:])
 
 	// TODO(bwplotka): This lock can lock all scrapers, there might high contention on this on scale.
 	// Optimize by moving the lock to be per series (& benchmark it).
@@ -213,7 +218,7 @@ func (ce *CircularExemplarStorage) ValidateExemplar(l labels.Labels, e exemplar.
 
 // Not thread safe. The append parameters tells us whether this is an external validation, or internal
 // as a result of an AddExemplar call, in which case we should update any relevant metrics.
-func (ce *CircularExemplarStorage) validateExemplar(l string, e exemplar.Exemplar, append bool) error {
+func (ce *CircularExemplarStorage) validateExemplar(key []byte, e exemplar.Exemplar, append bool) error {
 	if len(ce.exemplars) <= 0 {
 		return storage.ErrExemplarsDisabled
 	}
@@ -230,7 +235,7 @@ func (ce *CircularExemplarStorage) validateExemplar(l string, e exemplar.Exempla
 		}
 	}
 
-	idx, ok := ce.index[l]
+	idx, ok := ce.index[string(key)]
 	if !ok {
 		return nil
 	}
@@ -269,7 +274,7 @@ func (ce *CircularExemplarStorage) Resize(l int64) int {
 	oldNextIndex := int64(ce.nextIndex)
 
 	ce.exemplars = make([]*circularBufferEntry, l)
-	ce.index = make(map[string]*indexEntry)
+	ce.index = make(map[string]*indexEntry, l/estimatedExemplarsPerSeries)
 	ce.nextIndex = 0
 
 	// Replay as many entries as needed, starting with oldest first.
@@ -305,13 +310,14 @@ func (ce *CircularExemplarStorage) Resize(l int64) int {
 // migrate is like AddExemplar but reuses existing structs. Expected to be called in batch and requires
 // external lock and does not compute metrics.
 func (ce *CircularExemplarStorage) migrate(entry *circularBufferEntry) {
-	seriesLabels := entry.ref.seriesLabels.String()
+	var buf [1024]byte
+	seriesLabels := entry.ref.seriesLabels.Bytes(buf[:])
 
-	idx, ok := ce.index[seriesLabels]
+	idx, ok := ce.index[string(seriesLabels)]
 	if !ok {
 		idx = entry.ref
 		idx.oldest = ce.nextIndex
-		ce.index[seriesLabels] = idx
+		ce.index[string(seriesLabels)] = idx
 	} else {
 		entry.ref = idx
 		ce.exemplars[idx.newest].next = ce.nextIndex
@@ -329,7 +335,8 @@ func (ce *CircularExemplarStorage) AddExemplar(l labels.Labels, e exemplar.Exemp
 		return storage.ErrExemplarsDisabled
 	}
 
-	seriesLabels := l.String()
+	var buf [1024]byte
+	seriesLabels := l.Bytes(buf[:])
 
 	// TODO(bwplotka): This lock can lock all scrapers, there might high contention on this on scale.
 	// Optimize by moving the lock to be per series (& benchmark it).
@@ -345,11 +352,11 @@ func (ce *CircularExemplarStorage) AddExemplar(l labels.Labels, e exemplar.Exemp
 		return err
 	}
 
-	_, ok := ce.index[seriesLabels]
+	_, ok := ce.index[string(seriesLabels)]
 	if !ok {
-		ce.index[seriesLabels] = &indexEntry{oldest: ce.nextIndex, seriesLabels: l}
+		ce.index[string(seriesLabels)] = &indexEntry{oldest: ce.nextIndex, seriesLabels: l}
 	} else {
-		ce.exemplars[ce.index[seriesLabels].newest].next = ce.nextIndex
+		ce.exemplars[ce.index[string(seriesLabels)].newest].next = ce.nextIndex
 	}
 
 	if prev := ce.exemplars[ce.nextIndex]; prev == nil {
@@ -357,12 +364,13 @@ 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.ref.seriesLabels.String()
+		var buf [1024]byte
+		prevLabels := prev.ref.seriesLabels.Bytes(buf[:])
 		if prev.next == noExemplar {
 			// Last item for this series, remove index entry.
-			delete(ce.index, prevLabels)
+			delete(ce.index, string(prevLabels))
 		} else {
-			ce.index[prevLabels].oldest = prev.next
+			ce.index[string(prevLabels)].oldest = prev.next
 		}
 	}
 
@@ -370,8 +378,8 @@ func (ce *CircularExemplarStorage) AddExemplar(l labels.Labels, e exemplar.Exemp
 	// since this is the first exemplar stored for this series.
 	ce.exemplars[ce.nextIndex].next = noExemplar
 	ce.exemplars[ce.nextIndex].exemplar = e
-	ce.exemplars[ce.nextIndex].ref = ce.index[seriesLabels]
-	ce.index[seriesLabels].newest = ce.nextIndex
+	ce.exemplars[ce.nextIndex].ref = ce.index[string(seriesLabels)]
+	ce.index[string(seriesLabels)].newest = ce.nextIndex
 
 	ce.nextIndex = (ce.nextIndex + 1) % len(ce.exemplars)
 

tsdb/exemplar_test.go

@@ -112,7 +112,7 @@ func TestAddExemplar(t *testing.T) {
 	}
 
 	require.NoError(t, es.AddExemplar(l, e))
-	require.Equal(t, es.index[l.String()].newest, 0, "exemplar was not stored correctly")
+	require.Equal(t, es.index[string(l.Bytes(nil))].newest, 0, "exemplar was not stored correctly")
 
 	e2 := exemplar.Exemplar{
 		Labels: labels.Labels{
@@ -126,8 +126,8 @@ func TestAddExemplar(t *testing.T) {
 	}
 
 	require.NoError(t, es.AddExemplar(l, e2))
-	require.Equal(t, es.index[l.String()].newest, 1, "exemplar was not stored correctly, location of newest exemplar for series in index did not update")
-	require.True(t, es.exemplars[es.index[l.String()].newest].exemplar.Equals(e2), "exemplar was not stored correctly, expected %+v got: %+v", e2, es.exemplars[es.index[l.String()].newest].exemplar)
+	require.Equal(t, es.index[string(l.Bytes(nil))].newest, 1, "exemplar was not stored correctly, location of newest exemplar for series in index did not update")
+	require.True(t, es.exemplars[es.index[string(l.Bytes(nil))].newest].exemplar.Equals(e2), "exemplar was not stored correctly, expected %+v got: %+v", e2, es.exemplars[es.index[string(l.Bytes(nil))].newest].exemplar)
 
 	require.NoError(t, es.AddExemplar(l, e2), "no error is expected attempting to add duplicate exemplar")
 
@@ -300,7 +300,7 @@ func TestSelectExemplar_TimeRange(t *testing.T) {
 			Ts:    int64(101 + i),
 		})
 		require.NoError(t, err)
-		require.Equal(t, es.index[l.String()].newest, i, "exemplar was not stored correctly")
+		require.Equal(t, es.index[string(l.Bytes(nil))].newest, i, "exemplar was not stored correctly")
 	}
 
 	m, err := labels.NewMatcher(labels.MatchEqual, l[0].Name, l[0].Value)
@@ -376,14 +376,14 @@ func TestIndexOverwrite(t *testing.T) {
 
 	// Ensure index GC'ing is taking place, there should no longer be any
 	// index entry for series l1 since we just wrote two exemplars for series l2.
-	_, ok := es.index[l1.String()]
+	_, ok := es.index[string(l1.Bytes(nil))]
 	require.False(t, ok)
-	require.Equal(t, &indexEntry{1, 0, l2}, es.index[l2.String()])
+	require.Equal(t, &indexEntry{1, 0, l2}, es.index[string(l2.Bytes(nil))])
 
 	err = es.AddExemplar(l1, exemplar.Exemplar{Value: 4, Ts: 4})
 	require.NoError(t, err)
 
-	i := es.index[l2.String()]
+	i := es.index[string(l2.Bytes(nil))]
 	require.Equal(t, &indexEntry{0, 0, l2}, i)
 }
 
@@ -492,18 +492,23 @@ func BenchmarkAddExemplar(b *testing.B) {
 
 	for _, n := range []int{10000, 100000, 1000000} {
 		b.Run(fmt.Sprintf("%d", n), func(b *testing.B) {
-			exs, err := NewCircularExemplarStorage(int64(n), eMetrics)
-			require.NoError(b, err)
-			es := exs.(*CircularExemplarStorage)
-
-			b.ResetTimer()
-			l := labels.Labels{{Name: "service", Value: strconv.Itoa(0)}}
-			for i := 0; i < n; i++ {
-				if i%100 == 0 {
-					l = labels.Labels{{Name: "service", Value: strconv.Itoa(i)}}
-				}
-				err = es.AddExemplar(l, exemplar.Exemplar{Value: float64(i), Ts: int64(i), Labels: exLabels})
+			for j := 0; j < b.N; j++ {
+				b.StopTimer()
+				exs, err := NewCircularExemplarStorage(int64(n), eMetrics)
 				require.NoError(b, err)
+				es := exs.(*CircularExemplarStorage)
+				l := labels.Labels{{Name: "service", Value: strconv.Itoa(0)}}
+				b.StartTimer()
+
+				for i := 0; i < n; i++ {
+					if i%100 == 0 {
+						l = labels.Labels{{Name: "service", Value: strconv.Itoa(i)}}
+					}
+					err = es.AddExemplar(l, exemplar.Exemplar{Value: float64(i), Ts: int64(i), Labels: exLabels})
+					if err != nil {
+						require.NoError(b, err)
+					}
+				}
 			}
 		})
 	}
@@ -543,24 +548,24 @@ func BenchmarkResizeExemplars(b *testing.B) {
 	}
 
 	for _, tc := range testCases {
-		exs, err := NewCircularExemplarStorage(tc.startSize, eMetrics)
-		require.NoError(b, err)
-		es := exs.(*CircularExemplarStorage)
+		b.Run(fmt.Sprintf("%s-%d-to-%d", tc.name, tc.startSize, tc.endSize), func(b *testing.B) {
+			for j := 0; j < b.N; j++ {
+				b.StopTimer()
+				exs, err := NewCircularExemplarStorage(tc.startSize, eMetrics)
+				require.NoError(b, err)
+				es := exs.(*CircularExemplarStorage)
 
-		for i := 0; i < int(float64(tc.startSize)*float64(1.5)); i++ {
-			l := labels.FromStrings("service", strconv.Itoa(i))
+				for i := 0; i < int(float64(tc.startSize)*float64(1.5)); i++ {
+					l := labels.FromStrings("service", strconv.Itoa(i))
 
-			err = es.AddExemplar(l, exemplar.Exemplar{Value: float64(i), Ts: int64(i)})
-			require.NoError(b, err)
-		}
-		saveIndex := es.index
-		saveExemplars := es.exemplars
-
-		b.Run(fmt.Sprintf("%s-%d-to-%d", tc.name, tc.startSize, tc.endSize), func(t *testing.B) {
-			es.index = saveIndex
-			es.exemplars = saveExemplars
-			b.ResetTimer()
-			es.Resize(tc.endSize)
+					err = es.AddExemplar(l, exemplar.Exemplar{Value: float64(i), Ts: int64(i)})
+					if err != nil {
+						require.NoError(b, err)
+					}
+				}
+				b.StartTimer()
+				es.Resize(tc.endSize)
+			}
 		})
 	}
 }