feat(go): expose fast writer batch pending metrics

go/vehicle-gateway/cmd/nats-fast-writer/main.go

@@ -262,6 +262,8 @@ func processFastBatch(ctx context.Context, registry *metrics.Registry, appender
 	if len(envelopes) == 0 {
 		return nil
 	}
+	setFastBatchPending(registry, len(messages), len(envelopes))
+	defer setFastBatchPending(registry, 0, 0)
 	subject := fastBatchSubject(validMessages)
 	started := time.Now()
 	err := appender.AppendAllBatch(ctx, envelopes)
@@ -367,6 +369,14 @@ func addFastMetric(registry *metrics.Registry, subject string, status string) {
 	registry.IncCounter("vehicle_fast_writer_messages_total", metrics.Labels{"subject": subject, "status": status})
 }
 
+func setFastBatchPending(registry *metrics.Registry, messages int, envelopes int) {
+	if registry == nil {
+		return
+	}
+	registry.SetGauge("vehicle_fast_writer_batch_pending_messages", nil, float64(messages))
+	registry.SetGauge("vehicle_fast_writer_batch_pending_envelopes", nil, float64(envelopes))
+}
+
 func recordFastWriterStageDuration(registry *metrics.Registry, subject string, stage string, status string, elapsed time.Duration) {
 	if registry == nil {
 		return

go/vehicle-gateway/cmd/nats-fast-writer/main_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"strings"
+	"sync"
 	"testing"
 
 	"lingniu-vehicle-ingest/go/vehicle-gateway/internal/envelope"
@@ -113,11 +114,71 @@ func TestProcessFastBatchAppendsTDengineBatchBeforeRedisAndAck(t *testing.T) {
 	}
 }
 
+func TestProcessFastBatchExposesPendingMetricsDuringAppend(t *testing.T) {
+	first := envelope.FrameEnvelope{Protocol: envelope.ProtocolJT808, VIN: "VIN001", EventID: "evt-6"}
+	second := envelope.FrameEnvelope{Protocol: envelope.ProtocolJT808, VIN: "VIN002", EventID: "evt-7"}
+	firstPayload, err := first.MarshalJSONBytes()
+	if err != nil {
+		t.Fatal(err)
+	}
+	secondPayload, err := second.MarshalJSONBytes()
+	if err != nil {
+		t.Fatal(err)
+	}
+	registry := metrics.NewRegistry()
+	appenderStarted := make(chan struct{})
+	appenderRelease := make(chan struct{})
+	appender := &recordingFastAppender{
+		onAppendBatch: func() {
+			close(appenderStarted)
+			<-appenderRelease
+		},
+	}
+	msgs := []*fastMessage{
+		{subject: "vehicle.raw.go.jt808.v1", data: firstPayload, ack: func() error { return nil }},
+		{subject: "vehicle.raw.go.jt808.v1", data: secondPayload, ack: func() error { return nil }},
+	}
+	var wg sync.WaitGroup
+	wg.Add(1)
+	var processErr error
+	go func() {
+		defer wg.Done()
+		processErr = processFastBatch(context.Background(), registry, appender, &recordingFastUpdater{}, msgs)
+	}()
+	<-appenderStarted
+
+	text := registry.Render()
+	for _, want := range []string{
+		`vehicle_fast_writer_batch_pending_messages 2`,
+		`vehicle_fast_writer_batch_pending_envelopes 2`,
+	} {
+		if !strings.Contains(text, want) {
+			t.Fatalf("pending metric missing %s while appending:\n%s", want, text)
+		}
+	}
+
+	close(appenderRelease)
+	wg.Wait()
+	if processErr != nil {
+		t.Fatalf("processFastBatch() error = %v", processErr)
+	}
+	text = registry.Render()
+	for _, want := range []string{
+		`vehicle_fast_writer_batch_pending_messages 0`,
+		`vehicle_fast_writer_batch_pending_envelopes 0`,
+	} {
+		if !strings.Contains(text, want) {
+			t.Fatalf("pending metric should reset after append, missing %s:\n%s", want, text)
+		}
+	}
+}
+
 type recordingFastAppender struct {
-	count      int
-	batchCount int
-	batchRows  int
-	err        error
+	count         int
+	batchCount    int
+	batchRows     int
+	err           error
+	onAppendBatch func()
 }
 
 func (a *recordingFastAppender) AppendAll(context.Context, envelope.FrameEnvelope) error {
@@ -128,6 +189,9 @@ func (a *recordingFastAppender) AppendAll(context.Context, envelope.FrameEnvelop
 func (a *recordingFastAppender) AppendAllBatch(_ context.Context, envs []envelope.FrameEnvelope) error {
 	a.batchCount++
 	a.batchRows += len(envs)
+	if a.onAppendBatch != nil {
+		a.onAppendBatch()
+	}
 	return a.err
 }