Optimize SeriesGrouper & aggregators.merge (#8391)

The previous implementation of SeriesGrouper required breaking a metric object apart into its constituents, converting tags and keys into unoptimized maps, only to have it put them back together into another metric object. This resulted in a significant performance overhead. This overhead was further compounded when the number of fields was large.

This change adds a new AddMetric method to SeriesGrouper which preserves the metric object and removes the back-and-forth conversion.

Additionlly the method used for calculating the metric's hash was switched to use maphash, which is optimized for this case.

----

Benchmarks

Before:

    BenchmarkMergeOne-16          106012	     11790 ns/op
    BenchmarkMergeTwo-16           48529	     24819 ns/op
    BenchmarkGroupID-16           780018	      1608 ns/op

After:

    BenchmarkMergeOne-16          907093	      1173 ns/op
    BenchmarkMergeTwo-16          508321	      2168 ns/op
    BenchmarkGroupID-16         11217788	      99.4 ns/op

metric/series_grouper.go

@@ -1,10 +1,9 @@
 package metric
 
 import (
-	"hash/fnv"
-	"io"
+	"encoding/binary"
+	"hash/maphash"
 	"sort"
-	"strconv"
 	"time"
 
 	"github.com/influxdata/telegraf"
@@ -23,14 +22,17 @@ import (
 // + cpu,host=localhost idle_time=42,usage_time=42
 func NewSeriesGrouper() *SeriesGrouper {
 	return &SeriesGrouper{
-		metrics: make(map[uint64]telegraf.Metric),
-		ordered: []telegraf.Metric{},
+		metrics:  make(map[uint64]telegraf.Metric),
+		ordered:  []telegraf.Metric{},
+		hashSeed: maphash.MakeSeed(),
 	}
 }
 
 type SeriesGrouper struct {
 	metrics map[uint64]telegraf.Metric
 	ordered []telegraf.Metric
+
+	hashSeed maphash.Seed
 }
 
 // Add adds a field key and value to the series.
@@ -41,8 +43,15 @@ func (g *SeriesGrouper) Add(
 	field string,
 	fieldValue interface{},
 ) error {
+	taglist := make([]*telegraf.Tag, 0, len(tags))
+	for k, v := range tags {
+		taglist = append(taglist,
+			&telegraf.Tag{Key: k, Value: v})
+	}
+	sort.Slice(taglist, func(i, j int) bool { return taglist[i].Key < taglist[j].Key })
+
 	var err error
-	id := groupID(measurement, tags, tm)
+	id := groupID(g.hashSeed, measurement, taglist, tm)
 	metric := g.metrics[id]
 	if metric == nil {
 		metric, err = New(measurement, tags, map[string]interface{}{field: fieldValue}, tm)
@@ -57,30 +66,46 @@ func (g *SeriesGrouper) Add(
 	return nil
 }
 
+// AddMetric adds a metric to the series, merging with any previous matching metrics.
+func (g *SeriesGrouper) AddMetric(
+	metric telegraf.Metric,
+) {
+	id := groupID(g.hashSeed, metric.Name(), metric.TagList(), metric.Time())
+	m := g.metrics[id]
+	if m == nil {
+		m = metric.Copy()
+		g.metrics[id] = m
+		g.ordered = append(g.ordered, m)
+	} else {
+		for _, f := range metric.FieldList() {
+			m.AddField(f.Key, f.Value)
+		}
+	}
+}
+
 // Metrics returns the metrics grouped by series and time.
 func (g *SeriesGrouper) Metrics() []telegraf.Metric {
 	return g.ordered
 }
 
-func groupID(measurement string, tags map[string]string, tm time.Time) uint64 {
-	h := fnv.New64a()
-	h.Write([]byte(measurement))
-	h.Write([]byte("\n"))
+func groupID(seed maphash.Seed, measurement string, taglist []*telegraf.Tag, tm time.Time) uint64 {
+	var mh maphash.Hash
+	mh.SetSeed(seed)
+
+	mh.WriteString(measurement)
+	mh.WriteByte(0)
 
-	taglist := make([]*telegraf.Tag, 0, len(tags))
-	for k, v := range tags {
-		taglist = append(taglist,
-			&telegraf.Tag{Key: k, Value: v})
-	}
-	sort.Slice(taglist, func(i, j int) bool { return taglist[i].Key < taglist[j].Key })
 	for _, tag := range taglist {
-		h.Write([]byte(tag.Key))
-		h.Write([]byte("\n"))
-		h.Write([]byte(tag.Value))
-		h.Write([]byte("\n"))
+		mh.WriteString(tag.Key)
+		mh.WriteByte(0)
+		mh.WriteString(tag.Value)
+		mh.WriteByte(0)
 	}
-	h.Write([]byte("\n"))
+	mh.WriteByte(0)
 
-	io.WriteString(h, strconv.FormatInt(tm.UnixNano(), 10))
-	return h.Sum64()
+	var tsBuf [8]byte
+	binary.BigEndian.PutUint64(tsBuf[:], uint64(tm.UnixNano()))
+	mh.Write(tsBuf[:])
+
+	return mh.Sum64()
 }

metric/series_grouper_test.go

@@ -0,0 +1,37 @@
+package metric
+
+import (
+	"hash/maphash"
+	"testing"
+	"time"
+)
+
+var m, _ = New(
+	"mymetric",
+	map[string]string{
+		"host":        "host.example.com",
+		"mykey":       "myvalue",
+		"another key": "another value",
+	},
+	map[string]interface{}{
+		"f1": 1,
+		"f2": 2,
+		"f3": 3,
+		"f4": 4,
+		"f5": 5,
+		"f6": 6,
+		"f7": 7,
+		"f8": 8,
+	},
+	time.Now(),
+)
+
+var result uint64
+
+var hashSeed = maphash.MakeSeed()
+
+func BenchmarkGroupID(b *testing.B) {
+	for n := 0; n < b.N; n++ {
+		result = groupID(hashSeed, m.Name(), m.TagList(), m.Time())
+	}
+}

plugins/aggregators/merge/merge.go

@@ -36,13 +36,7 @@ func (a *Merge) SampleConfig() string {
 }
 
 func (a *Merge) Add(m telegraf.Metric) {
-	tags := m.Tags()
-	for _, field := range m.FieldList() {
-		err := a.grouper.Add(m.Name(), tags, m.Time(), field.Key, field.Value)
-		if err != nil {
-			a.log.Errorf("Error adding metric: %v", err)
-		}
-	}
+	a.grouper.AddMetric(m)
 }
 
 func (a *Merge) Push(acc telegraf.Accumulator) {

plugins/aggregators/merge/merge_test.go

@@ -4,9 +4,11 @@ import (
 	"testing"
 	"time"
 
-	"github.com/influxdata/telegraf"
-	"github.com/influxdata/telegraf/testutil"
 	"github.com/stretchr/testify/require"
+
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/metric"
+	"github.com/influxdata/telegraf/testutil"
 )
 
 func TestSimple(t *testing.T) {
@@ -184,3 +186,68 @@ func TestReset(t *testing.T) {
 
 	testutil.RequireMetricsEqual(t, expected, acc.GetTelegrafMetrics())
 }
+
+var m1, _ = metric.New(
+	"mymetric",
+	map[string]string{
+		"host":        "host.example.com",
+		"mykey":       "myvalue",
+		"another key": "another value",
+	},
+	map[string]interface{}{
+		"f1": 1,
+		"f2": 2,
+		"f3": 3,
+		"f4": 4,
+		"f5": 5,
+		"f6": 6,
+		"f7": 7,
+		"f8": 8,
+	},
+	time.Now(),
+)
+var m2, _ = metric.New(
+	"mymetric",
+	map[string]string{
+		"host":        "host.example.com",
+		"mykey":       "myvalue",
+		"another key": "another value",
+	},
+	map[string]interface{}{
+		"f8":  8,
+		"f9":  9,
+		"f10": 10,
+		"f11": 11,
+		"f12": 12,
+		"f13": 13,
+		"f14": 14,
+		"f15": 15,
+		"f16": 16,
+	},
+	m1.Time(),
+)
+
+func BenchmarkMergeOne(b *testing.B) {
+	var merger Merge
+	merger.Init()
+	var acc testutil.NopAccumulator
+
+	for n := 0; n < b.N; n++ {
+		merger.Reset()
+		merger.Add(m1)
+		merger.Push(&acc)
+	}
+}
+
+func BenchmarkMergeTwo(b *testing.B) {
+	var merger Merge
+	merger.Init()
+	var acc testutil.NopAccumulator
+
+	for n := 0; n < b.N; n++ {
+		merger.Reset()
+		merger.Add(m1)
+		merger.Add(m2)
+		merger.Push(&acc)
+	}
+}