feat(agent): Add metric disk buffer (#15564)

accumulator.go

@@ -57,6 +57,14 @@ type Accumulator interface {
 // TrackingID uniquely identifies a tracked metric group
 type TrackingID uint64
 
+type TrackingData interface {
+	// ID is the TrackingID
+	ID() TrackingID
+
+	// RefCount is the number of tracking metrics still persistent and referencing this tracking ID
+	RefCount() int32
+}
+
 // DeliveryInfo provides the results of a delivered metric group.
 type DeliveryInfo interface {
 	// ID is the TrackingID

config/config.go

@@ -278,6 +278,9 @@ type AgentConfig struct {
 	// Number of attempts to obtain a remote configuration via a URL during
 	// startup. Set to -1 for unlimited attempts.
 	ConfigURLRetryAttempts int `toml:"config_url_retry_attempts"`
+
+	BufferStrategy  string `toml:"buffer_strategy"`
+	BufferDirectory string `toml:"buffer_directory"`
 }
 
 // InputNames returns a list of strings of the configured inputs.
@@ -1521,6 +1524,8 @@ func (c *Config) buildOutput(name string, tbl *ast.Table) (*models.OutputConfig,
 	c.getFieldString(tbl, "name_suffix", &oc.NameSuffix)
 	c.getFieldString(tbl, "name_prefix", &oc.NamePrefix)
 	c.getFieldString(tbl, "startup_error_behavior", &oc.StartupErrorBehavior)
+	c.getFieldString(tbl, "buffer_strategy", &oc.BufferStrategy)
+	c.getFieldString(tbl, "buffer_directory", &oc.BufferDirectory)
 
 	if c.hasErrs() {
 		return nil, c.firstErr()

docs/LICENSE_OF_DEPENDENCIES.md

@@ -361,6 +361,8 @@ following works:
 - github.com/tidwall/gjson [MIT License](https://github.com/tidwall/gjson/blob/master/LICENSE)
 - github.com/tidwall/match [MIT License](https://github.com/tidwall/match/blob/master/LICENSE)
 - github.com/tidwall/pretty [MIT License](https://github.com/tidwall/pretty/blob/master/LICENSE)
+- github.com/tidwall/tinylru [MIT License](https://github.com/tidwall/tinylru/blob/master/LICENSE)
+- github.com/tidwall/wal [MIT License](https://github.com/tidwall/wal/blob/master/LICENSE)
 - github.com/tinylib/msgp [MIT License](https://github.com/tinylib/msgp/blob/master/LICENSE)
 - github.com/tklauser/go-sysconf [BSD 3-Clause "New" or "Revised" License](https://github.com/tklauser/go-sysconf/blob/master/LICENSE)
 - github.com/tklauser/numcpus [Apache License 2.0](https://github.com/tklauser/numcpus/blob/master/LICENSE)

go.mod

@@ -187,6 +187,7 @@ require (
 	github.com/testcontainers/testcontainers-go/modules/kafka v0.31.0
 	github.com/thomasklein94/packer-plugin-libvirt v0.5.0
 	github.com/tidwall/gjson v1.17.0
+	github.com/tidwall/wal v1.1.7
 	github.com/tinylib/msgp v1.2.0
 	github.com/urfave/cli/v2 v2.27.2
 	github.com/vapourismo/knx-go v0.0.0-20240217175130-922a0d50c241
@@ -461,6 +462,7 @@ require (
 	github.com/stretchr/objx v0.5.2 // indirect
 	github.com/tidwall/match v1.1.1 // indirect
 	github.com/tidwall/pretty v1.2.0 // indirect
+	github.com/tidwall/tinylru v1.1.0 // indirect
 	github.com/tklauser/go-sysconf v0.3.13 // indirect
 	github.com/tklauser/numcpus v0.7.0 // indirect
 	github.com/twmb/murmur3 v1.1.7 // indirect

go.sum

@@ -2336,12 +2336,17 @@ github.com/testcontainers/testcontainers-go/modules/kafka v0.31.0 h1:8B1u+sDwYhT
 github.com/testcontainers/testcontainers-go/modules/kafka v0.31.0/go.mod h1:W1+yLUfUl8VLTzvmApP2FBHgCk8I5SKKjDWjxWEc33U=
 github.com/thomasklein94/packer-plugin-libvirt v0.5.0 h1:aj2HLHZZM/ClGLIwVp9rrgh+2TOU/w4EiaZHAwCpOgs=
 github.com/thomasklein94/packer-plugin-libvirt v0.5.0/go.mod h1:GwN82FQ6KxCNKtS8LNUgLbwTZs90GGhBzCmTNkrTCrY=
+github.com/tidwall/gjson v1.10.2/go.mod h1:/wbyibRr2FHMks5tjHJ5F8dMZh3AcwJEMf5vlfC0lxk=
 github.com/tidwall/gjson v1.17.0 h1:/Jocvlh98kcTfpN2+JzGQWQcqrPQwDrVEMApx/M5ZwM=
 github.com/tidwall/gjson v1.17.0/go.mod h1:/wbyibRr2FHMks5tjHJ5F8dMZh3AcwJEMf5vlfC0lxk=
 github.com/tidwall/match v1.1.1 h1:+Ho715JplO36QYgwN9PGYNhgZvoUSc9X2c80KVTi+GA=
 github.com/tidwall/match v1.1.1/go.mod h1:eRSPERbgtNPcGhD8UCthc6PmLEQXEWd3PRB5JTxsfmM=
 github.com/tidwall/pretty v1.2.0 h1:RWIZEg2iJ8/g6fDDYzMpobmaoGh5OLl4AXtGUGPcqCs=
 github.com/tidwall/pretty v1.2.0/go.mod h1:ITEVvHYasfjBbM0u2Pg8T2nJnzm8xPwvNhhsoaGGjNU=
+github.com/tidwall/tinylru v1.1.0 h1:XY6IUfzVTU9rpwdhKUF6nQdChgCdGjkMfLzbWyiau6I=
+github.com/tidwall/tinylru v1.1.0/go.mod h1:3+bX+TJ2baOLMWTnlyNWHh4QMnFyARg2TLTQ6OFbzw8=
+github.com/tidwall/wal v1.1.7 h1:emc1TRjIVsdKKSnpwGBAcsAGg0767SvUk8+ygx7Bb+4=
+github.com/tidwall/wal v1.1.7/go.mod h1:r6lR1j27W9EPalgHiB7zLJDYu3mzW5BQP5KrzBpYY/E=
 github.com/tinylib/msgp v1.2.0 h1:0uKB/662twsVBpYUPbokj4sTSKhWFKB7LopO2kWK8lY=
 github.com/tinylib/msgp v1.2.0/go.mod h1:2vIGs3lcUo8izAATNobrCHevYZC/LMsJtw4JPiYPHro=
 github.com/tj/assert v0.0.0-20171129193455-018094318fb0/go.mod h1:mZ9/Rh9oLWpLLDRpvE+3b7gP/C2YyLFYxNmcLnPTMe0=

metric.go

@@ -149,5 +149,6 @@ type UnwrappableMetric interface {
 type TrackingMetric interface {
 	// TrackingID returns the ID used for tracking the metric
 	TrackingID() TrackingID
+	TrackingData() TrackingData
 	UnwrappableMetric
 }

metric/deserialize.go

@@ -0,0 +1,85 @@
+package metric
+
+import (
+	"bytes"
+	"encoding/gob"
+	"errors"
+	"fmt"
+	"sync"
+
+	"github.com/influxdata/telegraf"
+)
+
+// storage for tracking data that can't be serialized to disk
+var (
+	// grouped tracking metrics means that ID->Data association is not one to one,
+	// many metrics could be associated with one tracking ID so we cannot just
+	// clear this every time in FromBytes.
+	trackingStore = make(map[telegraf.TrackingID]telegraf.TrackingData)
+	mu            = sync.Mutex{}
+
+	// ErrSkipTracking indicates that tracking information could not be found after
+	// deserializing a metric from bytes. In this case we should skip the metric
+	// and continue as if it does not exist.
+	ErrSkipTracking = errors.New("metric tracking data not found")
+)
+
+type serializedMetric struct {
+	M   telegraf.Metric
+	TID telegraf.TrackingID
+}
+
+func ToBytes(m telegraf.Metric) ([]byte, error) {
+	var sm serializedMetric
+	if um, ok := m.(telegraf.UnwrappableMetric); ok {
+		sm.M = um.Unwrap()
+	} else {
+		sm.M = m
+	}
+
+	if tm, ok := m.(telegraf.TrackingMetric); ok {
+		sm.TID = tm.TrackingID()
+
+		mu.Lock()
+		trackingStore[sm.TID] = tm.TrackingData()
+		mu.Unlock()
+	}
+
+	var buf bytes.Buffer
+	encoder := gob.NewEncoder(&buf)
+	if err := encoder.Encode(&sm); err != nil {
+		return nil, fmt.Errorf("failed to encode metric to bytes: %w", err)
+	}
+	return buf.Bytes(), nil
+}
+
+func FromBytes(b []byte) (telegraf.Metric, error) {
+	buf := bytes.NewBuffer(b)
+	decoder := gob.NewDecoder(buf)
+
+	var sm *serializedMetric
+	if err := decoder.Decode(&sm); err != nil {
+		return nil, fmt.Errorf("failed to decode metric from bytes: %w", err)
+	}
+
+	m := sm.M
+	if sm.TID != 0 {
+		mu.Lock()
+		td := trackingStore[sm.TID]
+		if td == nil {
+			mu.Unlock()
+			return nil, ErrSkipTracking
+		}
+		rc := td.RefCount()
+		if rc <= 1 {
+			// only 1 metric left referencing this tracking ID, we can remove here since no subsequent metrics
+			// read can use this ID. If another metric in a metric group with this ID gets added later, it will
+			// simply be added back into the tracking store again.
+			trackingStore[sm.TID] = nil
+		}
+		mu.Unlock()
+
+		m = rebuildTrackingMetric(m, td)
+	}
+	return m, nil
+}

metric/init.go

@@ -0,0 +1,7 @@
+package metric
+
+import "encoding/gob"
+
+func Init() {
+	gob.RegisterName("metric.metric", &metric{})
+}

metric/tracking.go

@@ -33,35 +33,40 @@ func newTrackingID() telegraf.TrackingID {
 }
 
 type trackingData struct {
-	id          telegraf.TrackingID
-	rc          int32
-	acceptCount int32
-	rejectCount int32
+	//nolint:revive // method is already named ID
+	Id          telegraf.TrackingID
+	Rc          int32
+	AcceptCount int32
+	RejectCount int32
 	notifyFunc  NotifyFunc
 }
 
 func (d *trackingData) incr() {
-	atomic.AddInt32(&d.rc, 1)
+	atomic.AddInt32(&d.Rc, 1)
+}
+
+func (d *trackingData) RefCount() int32 {
+	return d.Rc
 }
 
 func (d *trackingData) decr() int32 {
-	return atomic.AddInt32(&d.rc, -1)
+	return atomic.AddInt32(&d.Rc, -1)
 }
 
 func (d *trackingData) accept() {
-	atomic.AddInt32(&d.acceptCount, 1)
+	atomic.AddInt32(&d.AcceptCount, 1)
 }
 
 func (d *trackingData) reject() {
-	atomic.AddInt32(&d.rejectCount, 1)
+	atomic.AddInt32(&d.RejectCount, 1)
 }
 
 func (d *trackingData) notify() {
 	d.notifyFunc(
 		&deliveryInfo{
-			id:       d.id,
-			accepted: int(d.acceptCount),
-			rejected: int(d.rejectCount),
+			id:       d.Id,
+			accepted: int(d.AcceptCount),
+			rejected: int(d.RejectCount),
 		},
 	)
 }
@@ -75,10 +80,10 @@ func newTrackingMetric(metric telegraf.Metric, fn NotifyFunc) (telegraf.Metric,
 	m := &trackingMetric{
 		Metric: metric,
 		d: &trackingData{
-			id:          newTrackingID(),
-			rc:          1,
-			acceptCount: 0,
-			rejectCount: 0,
+			Id:          newTrackingID(),
+			Rc:          1,
+			AcceptCount: 0,
+			RejectCount: 0,
 			notifyFunc:  fn,
 		},
 	}
@@ -86,15 +91,22 @@ func newTrackingMetric(metric telegraf.Metric, fn NotifyFunc) (telegraf.Metric,
 	if finalizer != nil {
 		runtime.SetFinalizer(m.d, finalizer)
 	}
-	return m, m.d.id
+	return m, m.d.Id
+}
+
+func rebuildTrackingMetric(metric telegraf.Metric, td telegraf.TrackingData) telegraf.Metric {
+	return &trackingMetric{
+		Metric: metric,
+		d:      td.(*trackingData),
+	}
 }
 
 func newTrackingMetricGroup(group []telegraf.Metric, fn NotifyFunc) ([]telegraf.Metric, telegraf.TrackingID) {
 	d := &trackingData{
-		id:          newTrackingID(),
-		rc:          0,
-		acceptCount: 0,
-		rejectCount: 0,
+		Id:          newTrackingID(),
+		Rc:          0,
+		AcceptCount: 0,
+		RejectCount: 0,
 		notifyFunc:  fn,
 	}
 
@@ -114,7 +126,7 @@ func newTrackingMetricGroup(group []telegraf.Metric, fn NotifyFunc) ([]telegraf.
 		d.notify()
 	}
 
-	return group, d.id
+	return group, d.Id
 }
 
 func (m *trackingMetric) Copy() telegraf.Metric {
@@ -152,7 +164,11 @@ func (m *trackingMetric) decr() {
 
 // Unwrap allows to access the underlying metric directly e.g. for go-templates
 func (m *trackingMetric) TrackingID() telegraf.TrackingID {
-	return m.d.id
+	return m.d.Id
+}
+
+func (m *trackingMetric) TrackingData() telegraf.TrackingData {
+	return m.d
 }
 
 // Unwrap allows to access the underlying metric directly e.g. for go-templates
@@ -173,3 +189,7 @@ func (r *deliveryInfo) ID() telegraf.TrackingID {
 func (r *deliveryInfo) Delivered() bool {
 	return r.rejected == 0
 }
+
+func (d *trackingData) ID() telegraf.TrackingID {
+	return d.Id
+}

models/buffer.go

@@ -2,14 +2,18 @@ package models
 
 import (
 	"fmt"
+	"sync"
 
 	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/metric"
 	"github.com/influxdata/telegraf/selfstat"
 )
 
 var (
 	AgentMetricsWritten = selfstat.Register("agent", "metrics_written", map[string]string{})
 	AgentMetricsDropped = selfstat.Register("agent", "metrics_dropped", map[string]string{})
+
+	registerGob = sync.OnceFunc(func() { metric.Init() })
 )
 
 type Buffer interface {
@@ -45,12 +49,16 @@ type BufferStats struct {
 }
 
 // NewBuffer returns a new empty Buffer with the given capacity.
-func NewBuffer(name string, alias string, capacity int, strategy string, _ string) (Buffer, error) {
+func NewBuffer(name string, alias string, capacity int, strategy string, path string) (Buffer, error) {
+	registerGob()
+
 	bs := NewBufferStats(name, alias, capacity)
 
 	switch strategy {
 	case "", "memory":
 		return NewMemoryBuffer(capacity, bs)
+	case "disk":
+		return NewDiskBuffer(name, path, bs)
 	}
 	return nil, fmt.Errorf("invalid buffer strategy %q", strategy)
 }
@@ -97,14 +105,14 @@ func (b *BufferStats) metricAdded() {
 	b.MetricsAdded.Incr(1)
 }
 
-func (b *BufferStats) metricWritten(metric telegraf.Metric) {
+func (b *BufferStats) metricWritten(m telegraf.Metric) {
 	AgentMetricsWritten.Incr(1)
 	b.MetricsWritten.Incr(1)
-	metric.Accept()
+	m.Accept()
 }
 
-func (b *BufferStats) metricDropped(metric telegraf.Metric) {
+func (b *BufferStats) metricDropped(m telegraf.Metric) {
 	AgentMetricsDropped.Incr(1)
 	b.MetricsDropped.Incr(1)
-	metric.Reject()
+	m.Reject()
 }

models/buffer_disk.go

@@ -0,0 +1,216 @@
+package models
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sync"
+
+	"github.com/tidwall/wal"
+
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/metric"
+)
+
+type DiskBuffer struct {
+	BufferStats
+	sync.Mutex
+
+	file *wal.Log
+	path string
+
+	batchFirst uint64 // Index of the first metric in the batch
+	batchSize  uint64 // Number of metrics currently in the batch
+
+	// Ending point of metrics read from disk on telegraf launch.
+	// Used to know whether to discard tracking metrics.
+	originalEnd uint64
+}
+
+func NewDiskBuffer(name string, path string, stats BufferStats) (*DiskBuffer, error) {
+	filePath := filepath.Join(path, name)
+	walFile, err := wal.Open(filePath, nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open wal file: %w", err)
+	}
+	buf := &DiskBuffer{
+		BufferStats: stats,
+		file:        walFile,
+		path:        filePath,
+	}
+	if buf.length() > 0 {
+		buf.originalEnd = buf.writeIndex()
+	}
+	return buf, nil
+}
+
+func (b *DiskBuffer) Len() int {
+	b.Lock()
+	defer b.Unlock()
+	return b.length()
+}
+
+func (b *DiskBuffer) length() int {
+	// Special case for when the read index is zero, it must be empty (otherwise it would be >= 1)
+	if b.readIndex() == 0 {
+		return 0
+	}
+	return int(b.writeIndex() - b.readIndex())
+}
+
+// readIndex is the first index to start reading metrics from, or the head of the buffer
+func (b *DiskBuffer) readIndex() uint64 {
+	index, err := b.file.FirstIndex()
+	if err != nil {
+		panic(err) // can only occur with a corrupt wal file
+	}
+	return index
+}
+
+// writeIndex is the first index to start writing metrics to, or the tail of the buffer
+func (b *DiskBuffer) writeIndex() uint64 {
+	index, err := b.file.LastIndex()
+	if err != nil {
+		panic(err) // can only occur with a corrupt wal file
+	}
+	return index + 1
+}
+
+func (b *DiskBuffer) Add(metrics ...telegraf.Metric) int {
+	b.Lock()
+	defer b.Unlock()
+
+	dropped := 0
+	for _, m := range metrics {
+		if !b.addSingleMetric(m) {
+			dropped++
+		}
+	}
+	b.BufferSize.Set(int64(b.length()))
+	return dropped
+}
+
+func (b *DiskBuffer) addSingleMetric(m telegraf.Metric) bool {
+	data, err := metric.ToBytes(m)
+	if err != nil {
+		panic(err)
+	}
+	err = b.file.Write(b.writeIndex(), data)
+	if err == nil {
+		b.metricAdded()
+		return true
+	}
+	return false
+}
+
+func (b *DiskBuffer) Batch(batchSize int) []telegraf.Metric {
+	b.Lock()
+	defer b.Unlock()
+
+	if b.length() == 0 {
+		// no metrics in the wal file, so return an empty array
+		return []telegraf.Metric{}
+	}
+	b.batchFirst = b.readIndex()
+	var metrics []telegraf.Metric
+
+	b.batchSize = 0
+	readIndex := b.batchFirst
+	endIndex := b.writeIndex()
+	for batchSize > 0 && readIndex < endIndex {
+		data, err := b.file.Read(readIndex)
+		if err != nil {
+			panic(err)
+		}
+		readIndex++
+
+		m, err := metric.FromBytes(data)
+
+		// Validate that a tracking metric is from this instance of telegraf and skip ones from older instances.
+		// A tracking metric can be skipped here because metric.Accept() is only called once data is successfully
+		// written to an output, so any tracking metrics from older instances can be dropped and reacquired to
+		// have an accurate tracking information.
+		// There are two primary cases here:
+		// - ErrSkipTracking:  means that the tracking information was unable to be found for a tracking ID.
+		// - Outside of range: means that the metric was guaranteed to be left over from the previous instance
+		//                     as it was here when we opened the wal file in this instance.
+		if errors.Is(err, metric.ErrSkipTracking) {
+			// could not look up tracking information for metric, skip
+			continue
+		}
+		if err != nil {
+			// non-recoverable error in deserialization, abort
+			panic(err)
+		}
+		if _, ok := m.(telegraf.TrackingMetric); ok && readIndex < b.originalEnd {
+			// tracking metric left over from previous instance, skip
+			continue
+		}
+
+		metrics = append(metrics, m)
+		b.batchSize++
+		batchSize--
+	}
+	return metrics
+}
+
+func (b *DiskBuffer) Accept(batch []telegraf.Metric) {
+	b.Lock()
+	defer b.Unlock()
+
+	if b.batchSize == 0 || len(batch) == 0 {
+		// nothing to accept
+		return
+	}
+	for _, m := range batch {
+		b.metricWritten(m)
+	}
+	if b.length() == len(batch) {
+		b.resetWalFile()
+	} else {
+		err := b.file.TruncateFront(b.batchFirst + uint64(len(batch)))
+		if err != nil {
+			panic(err)
+		}
+	}
+
+	// check if the original end index is still valid, clear if not
+	if b.originalEnd < b.readIndex() {
+		b.originalEnd = 0
+	}
+
+	b.resetBatch()
+	b.BufferSize.Set(int64(b.length()))
+}
+
+func (b *DiskBuffer) Reject(_ []telegraf.Metric) {
+	// very little to do here as the disk buffer retains metrics in
+	// the wal file until a call to accept
+	b.Lock()
+	defer b.Unlock()
+	b.resetBatch()
+}
+
+func (b *DiskBuffer) Stats() BufferStats {
+	return b.BufferStats
+}
+
+func (b *DiskBuffer) resetBatch() {
+	b.batchFirst = 0
+	b.batchSize = 0
+}
+
+// This is very messy and not ideal, but serves as the only way I can find currently
+// to actually clear the walfile completely if needed, since Truncate() calls require
+// that at least one entry remains in them otherwise they return an error.
+// Related issue: https://github.com/tidwall/wal/issues/20
+func (b *DiskBuffer) resetWalFile() {
+	b.file.Close()
+	os.Remove(b.path)
+	walFile, err := wal.Open(b.path, nil)
+	if err != nil {
+		panic(err)
+	}
+	b.file = walFile
+}

models/buffer_disk_test.go

@@ -0,0 +1,110 @@
+package models
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+	"github.com/tidwall/wal"
+
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/metric"
+	"github.com/influxdata/telegraf/testutil"
+)
+
+func newTestDiskBuffer(t testing.TB) Buffer {
+	path, err := os.MkdirTemp("", "*-buffer-test")
+	require.NoError(t, err)
+	return newTestDiskBufferWithPath(t, "test", path)
+}
+
+func newTestDiskBufferWithPath(t testing.TB, name string, path string) Buffer {
+	t.Helper()
+	buf, err := NewBuffer(name, "", 0, "disk", path)
+	require.NoError(t, err)
+	buf.Stats().MetricsAdded.Set(0)
+	buf.Stats().MetricsWritten.Set(0)
+	buf.Stats().MetricsDropped.Set(0)
+	return buf
+}
+
+func TestBuffer_RetainsTrackingInformation(t *testing.T) {
+	var delivered int
+	mm, _ := metric.WithTracking(Metric(), func(_ telegraf.DeliveryInfo) {
+		delivered++
+	})
+	b := newTestDiskBuffer(t)
+	b.Add(mm)
+	batch := b.Batch(1)
+	b.Accept(batch)
+	require.Equal(t, 1, delivered)
+}
+
+func TestBuffer_TrackingDroppedFromOldWal(t *testing.T) {
+	path, err := os.MkdirTemp("", "*-buffer-test")
+	require.NoError(t, err)
+	walfile, err := wal.Open(path, nil)
+	require.NoError(t, err)
+
+	tm, _ := metric.WithTracking(Metric(), func(_ telegraf.DeliveryInfo) {})
+
+	metrics := []telegraf.Metric{
+		// Basic metric with 1 field, 0 timestamp
+		Metric(),
+		// Basic metric with 1 field, different timestamp
+		metric.New(
+			"cpu",
+			map[string]string{},
+			map[string]interface{}{
+				"value": 20.0,
+			},
+			time.Now(),
+		),
+		// Metric with a field
+		metric.New(
+			"cpu",
+			map[string]string{
+				"x": "y",
+			},
+			map[string]interface{}{
+				"value": 18.0,
+			},
+			time.Now(),
+		),
+		// Tracking metric
+		tm,
+		// Metric with lots of tag types
+		metric.New(
+			"cpu",
+			map[string]string{},
+			map[string]interface{}{
+				"value_f64":        20.0,
+				"value_uint64":     uint64(10),
+				"value_int16":      int16(5),
+				"value_string":     "foo",
+				"value_boolean":    true,
+				"value_byte_array": []byte{1, 2, 3, 4, 5},
+			},
+			time.Now(),
+		),
+	}
+
+	// call manually so that we can properly use metric.ToBytes() without having initialized a buffer
+	registerGob()
+
+	for i, m := range metrics {
+		data, err := metric.ToBytes(m)
+		require.NoError(t, err)
+		require.NoError(t, walfile.Write(uint64(i+1), data))
+	}
+
+	b := newTestDiskBufferWithPath(t, filepath.Base(path), filepath.Dir(path))
+	batch := b.Batch(4)
+	// expected skips the tracking metric
+	expected := []telegraf.Metric{
+		metrics[0], metrics[1], metrics[2], metrics[4],
+	}
+	testutil.RequireMetricsEqual(t, expected, batch)
+}

models/buffer_mem_test.go

@@ -16,6 +16,21 @@ func newTestMemoryBuffer(t testing.TB, capacity int) Buffer {
 	return buf
 }
 
+func TestBuffer_AcceptCallsMetricAccept(t *testing.T) {
+	var accept int
+	mm := &MockMetric{
+		Metric: Metric(),
+		AcceptF: func() {
+			accept++
+		},
+	}
+	b := newTestMemoryBuffer(t, 5)
+	b.Add(mm, mm, mm)
+	batch := b.Batch(2)
+	b.Accept(batch)
+	require.Equal(t, 2, accept)
+}
+
 func BenchmarkAddMetrics(b *testing.B) {
 	buf := newTestMemoryBuffer(b, 10000)
 	m := Metric()

models/buffer_suite_test.go

@@ -43,6 +43,11 @@ func (s *BufferSuiteTest) SetupTest() {
 	switch s.bufferType {
 	case "", "memory":
 		s.hasMaxCapacity = true
+	case "disk":
+		path, err := os.MkdirTemp("", "*-buffer-test")
+		s.Require().NoError(err)
+		s.bufferPath = path
+		s.hasMaxCapacity = false
 	}
 }
 
@@ -57,6 +62,10 @@ func TestMemoryBufferSuite(t *testing.T) {
 	suite.Run(t, &BufferSuiteTest{bufferType: "memory"})
 }
 
+func TestDiskBufferSuite(t *testing.T) {
+	suite.Run(t, &BufferSuiteTest{bufferType: "disk"})
+}
+
 func Metric() telegraf.Metric {
 	return MetricTime(0)
 }
@@ -671,21 +680,6 @@ func (s *BufferSuiteTest) TestBuffer_BatchRejectAcceptNoop() {
 	s.Equal(5, b.Len())
 }
 
-func (s *BufferSuiteTest) TestBuffer_AcceptCallsMetricAccept() {
-	var accept int
-	mm := &MockMetric{
-		Metric: Metric(),
-		AcceptF: func() {
-			accept++
-		},
-	}
-	b := s.newTestBuffer(5)
-	b.Add(mm, mm, mm)
-	batch := b.Batch(2)
-	b.Accept(batch)
-	s.Equal(2, accept)
-}
-
 func (s *BufferSuiteTest) TestBuffer_AddCallsMetricRejectWhenNoBatch() {
 	if !s.hasMaxCapacity {
 		s.T().Skip("tested buffer does not have a maximum capacity")