Report metric about current size of the exporter retry queue

This commit adds observability to queue_retry exporter helper. It adds the first metric "queue_length" that indicates current size of the queue per exporter. The metrics is updated every second.

This is the first commit to address the issue open-telemetry#2434

exporter/exporterhelper/common.go

@@ -186,8 +186,7 @@ func (be *baseExporter) Start(ctx context.Context, host component.Host) error {
 	}
 
 	// If no error then start the queuedRetrySender.
-	be.qrSender.start()
-	return nil
+	return be.qrSender.start()
 }
 
 // Shutdown all senders and exporter and is invoked during service shutdown.

exporter/exporterhelper/common_test.go

@@ -19,6 +19,7 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/require"
+	"go.opencensus.io/tag"
 	"go.opencensus.io/trace"
 	"go.uber.org/zap"
 
@@ -27,12 +28,20 @@ import (
 	"go.opentelemetry.io/collector/config"
 )
 
-var okStatus = trace.Status{Code: trace.StatusCodeOK}
+var (
+	okStatus = trace.Status{Code: trace.StatusCodeOK}
 
-var defaultExporterCfg = &config.ExporterSettings{
-	TypeVal: "test",
-	NameVal: "test",
-}
+	defaultExporterName = "test"
+	defaultExporterCfg  = &config.ExporterSettings{
+		TypeVal: "test",
+		NameVal: defaultExporterName,
+	}
+
+	exporterTag, _      = tag.NewKey("exporter")
+	defautlExporterTags = []tag.Tag{
+		{Key: exporterTag, Value: defaultExporterName},
+	}
+)
 
 func TestErrorToStatus(t *testing.T) {
 	require.Equal(t, okStatus, errToStatus(nil))

exporter/exporterhelper/queued_retry.go

@@ -22,6 +22,9 @@ import (
 
 	"github.com/cenkalti/backoff/v4"
 	"github.com/jaegertracing/jaeger/pkg/queue"
+	"go.opencensus.io/metric"
+	"go.opencensus.io/metric/metricdata"
+	"go.opencensus.io/metric/metricproducer"
 	"go.opencensus.io/trace"
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
@@ -30,6 +33,20 @@ import (
 	"go.opentelemetry.io/collector/obsreport"
 )
 
+var (
+	r = metric.NewRegistry()
+
+	queueSizeGauge, _ = r.AddInt64DerivedGauge(
+		obsreport.ExporterKey+"/queue_size",
+		metric.WithDescription("Current size of the retry queue (in batches)"),
+		metric.WithLabelKeys(obsreport.ExporterKey),
+		metric.WithUnit(metricdata.UnitDimensionless))
+)
+
+func init() {
+	metricproducer.GlobalManager().AddProducer(r)
+}
+
 // QueueSettings defines configuration for queueing batches before sending to the consumerSender.
 type QueueSettings struct {
 	// Enabled indicates whether to not enqueue batches before sending to the consumerSender.
@@ -79,6 +96,7 @@ func DefaultRetrySettings() RetrySettings {
 }
 
 type queuedRetrySender struct {
+	fullName        string
 	cfg             QueueSettings
 	consumerSender  requestSender
 	queue           *queue.BoundedQueue
@@ -111,7 +129,8 @@ func newQueuedRetrySender(fullName string, qCfg QueueSettings, rCfg RetrySetting
 	sampledLogger := createSampledLogger(logger)
 	traceAttr := trace.StringAttribute(obsreport.ExporterKey, fullName)
 	return &queuedRetrySender{
-		cfg: qCfg,
+		fullName: fullName,
+		cfg:      qCfg,
 		consumerSender: &retrySender{
 			traceAttribute: traceAttr,
 			cfg:            rCfg,
@@ -127,11 +146,23 @@ func newQueuedRetrySender(fullName string, qCfg QueueSettings, rCfg RetrySetting
 }
 
 // start is invoked during service startup.
-func (qrs *queuedRetrySender) start() {
+func (qrs *queuedRetrySender) start() error {
 	qrs.queue.StartConsumers(qrs.cfg.NumConsumers, func(item interface{}) {
 		req := item.(request)
 		_ = qrs.consumerSender.send(req)
 	})
+
+	// Start reporting queue length metric
+	if qrs.cfg.Enabled {
+		err := queueSizeGauge.UpsertEntry(func() int64 {
+			return int64(qrs.queue.Size())
+		}, metricdata.NewLabelValue(qrs.fullName))
+		if err != nil {
+			return fmt.Errorf("failed to create retry queue size metric: %v", err)
+		}
+	}
+
+	return nil
 }
 
 // send implements the requestSender interface
@@ -167,6 +198,13 @@ func (qrs *queuedRetrySender) send(req request) error {
 
 // shutdown is invoked during service shutdown.
 func (qrs *queuedRetrySender) shutdown() {
+	// Cleanup queue metrics reporting
+	if qrs.cfg.Enabled {
+		_ = queueSizeGauge.UpsertEntry(func() int64 {
+			return int64(0)
+		}, metricdata.NewLabelValue(qrs.fullName))
+	}
+
 	// First stop the retry goroutines, so that unblocks the queue workers.
 	close(qrs.retryStopCh)
 

exporter/exporterhelper/queued_retry_test.go

@@ -17,13 +17,17 @@ package exporterhelper
 import (
 	"context"
 	"errors"
+	"fmt"
 	"sync"
 	"sync/atomic"
 	"testing"
 	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"go.opencensus.io/metric/metricdata"
+	"go.opencensus.io/metric/metricproducer"
+	"go.opencensus.io/tag"
 	"go.uber.org/zap"
 
 	"go.opentelemetry.io/collector/component/componenttest"
@@ -315,6 +319,23 @@ func TestQueuedRetryHappyPath(t *testing.T) {
 	ocs.checkDroppedItemsCount(t, 0)
 }
 
+func TestQueuedRetry_QueueMetricsReported(t *testing.T) {
+	qCfg := DefaultQueueSettings()
+	qCfg.NumConsumers = 0 // to make every request go straight to the queue
+	rCfg := DefaultRetrySettings()
+	be := newBaseExporter(defaultExporterCfg, zap.NewNop(), WithRetry(rCfg), WithQueue(qCfg))
+	require.NoError(t, be.Start(context.Background(), componenttest.NewNopHost()))
+	t.Cleanup(func() {
+		assert.NoError(t, be.Shutdown(context.Background()))
+	})
+
+	for i := 0; i < 7; i++ {
+		be.sender.send(newErrorRequest(context.Background()))
+	}
+
+	checkValueForProducer(t, defautlExporterTags, int64(7), "exporter/queue_size")
+}
+
 func TestNoCancellationContext(t *testing.T) {
 	deadline := time.Now().Add(1 * time.Second)
 	ctx, cancelFunc := context.WithDeadline(context.Background(), deadline)
@@ -440,3 +461,40 @@ func (ocs *observabilityConsumerSender) checkSendItemsCount(t *testing.T, want i
 func (ocs *observabilityConsumerSender) checkDroppedItemsCount(t *testing.T, want int) {
 	assert.EqualValues(t, want, atomic.LoadInt64(&ocs.droppedItemsCount))
 }
+
+// checkValueForProducer checks that the given metrics with wantTags is reported by one of the
+// metric producers
+func checkValueForProducer(t *testing.T, wantTags []tag.Tag, value int64, vName string) {
+	producers := metricproducer.GlobalManager().GetAll()
+	for _, producer := range producers {
+		for _, metric := range producer.Read() {
+			if metric.Descriptor.Name == vName && len(metric.TimeSeries) > 0 {
+				lastValue := metric.TimeSeries[len(metric.TimeSeries)-1]
+				if tagsMatchLabelKeys(wantTags, metric.Descriptor.LabelKeys, lastValue.LabelValues) {
+					require.Equal(t, value, lastValue.Points[len(lastValue.Points)-1].Value.(int64))
+					return
+				}
+
+			}
+		}
+	}
+
+	require.Fail(t, fmt.Sprintf("could not find metric %v with tags %s reported", vName, wantTags))
+}
+
+// tagsMatchLabelKeys returns true if provided tags match keys and values
+func tagsMatchLabelKeys(tags []tag.Tag, keys []metricdata.LabelKey, labels []metricdata.LabelValue) bool {
+	if len(tags) != len(keys) {
+		return false
+	}
+	for i := 0; i < len(tags); i++ {
+		var labelVal string
+		if labels[i].Present {
+			labelVal = labels[i].Value
+		}
+		if tags[i].Key.Name() != keys[i].Key || tags[i].Value != labelVal {
+			return false
+		}
+	}
+	return true
+}