perf(go): deduplicate unchanged mileage samples

go/vehicle-gateway/internal/stats/daily_metric.go

@@ -4,8 +4,10 @@ import (
 	"context"
 	"database/sql"
 	"errors"
+	"fmt"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 
 	"lingniu-vehicle-ingest/go/vehicle-gateway/internal/envelope"
@@ -16,8 +18,10 @@ type Execer interface {
 }
 
 type Writer struct {
-	exec Execer
-	loc  *time.Location
+	exec             Execer
+	loc              *time.Location
+	mu               sync.Mutex
+	lastTotalMileage map[string]float64
 }
 
 type MetricSample struct {
@@ -34,7 +38,7 @@ func NewWriter(exec Execer, loc *time.Location) *Writer {
 	if loc == nil {
 		loc = time.FixedZone("Asia/Shanghai", 8*3600)
 	}
-	return &Writer{exec: exec, loc: loc}
+	return &Writer{exec: exec, loc: loc, lastTotalMileage: map[string]float64{}}
 }
 
 func (w *Writer) EnsureSchema(ctx context.Context) error {
@@ -50,6 +54,9 @@ func (w *Writer) Append(ctx context.Context, env envelope.FrameEnvelope) error {
 		return err
 	}
 	for _, sample := range samples {
+		if w.seenSameMileage(sample) {
+			continue
+		}
 		if _, err := w.exec.ExecContext(ctx, upsertDailyMileageSQL,
 			sample.VIN,
 			sample.StatDate,
@@ -62,6 +69,23 @@ func (w *Writer) Append(ctx context.Context, env envelope.FrameEnvelope) error {
 	return nil
 }
 
+func (w *Writer) seenSameMileage(sample MetricSample) bool {
+	prefix := fmt.Sprintf("%s|%s|", sample.VIN, sample.Protocol)
+	key := prefix + sample.StatDate
+	w.mu.Lock()
+	defer w.mu.Unlock()
+	if last, ok := w.lastTotalMileage[key]; ok && last == sample.TotalMileageKM {
+		return true
+	}
+	for existing := range w.lastTotalMileage {
+		if strings.HasPrefix(existing, prefix) && existing != key {
+			delete(w.lastTotalMileage, existing)
+		}
+	}
+	w.lastTotalMileage[key] = sample.TotalMileageKM
+	return false
+}
+
 func SamplesFromEnvelope(env envelope.FrameEnvelope, loc *time.Location) ([]MetricSample, error) {
 	vin := strings.TrimSpace(env.VIN)
 	if vin == "" {

go/vehicle-gateway/internal/stats/daily_metric_test.go

@@ -149,6 +149,59 @@ func TestWriterEnsuresSchemaAndUpsertsDailyMileage(t *testing.T) {
 	}
 }
 
+func TestWriterSkipsConsecutiveDuplicateMileageSamples(t *testing.T) {
+	exec := &recordingExec{}
+	writer := NewWriter(exec, time.FixedZone("Asia/Shanghai", 8*3600))
+	event := envelope.FrameEnvelope{
+		Protocol:    envelope.ProtocolJT808,
+		VIN:         "LNBVIN00000000001",
+		EventTimeMS: time.Date(2026, 7, 1, 9, 0, 0, 0, time.FixedZone("Asia/Shanghai", 8*3600)).UnixMilli(),
+		Fields: map[string]any{
+			envelope.FieldTotalMileageKM: 10241.2,
+		},
+	}
+
+	if err := writer.Append(context.Background(), event); err != nil {
+		t.Fatalf("first Append() error = %v", err)
+	}
+	event.ReceivedAtMS += 1000
+	if err := writer.Append(context.Background(), event); err != nil {
+		t.Fatalf("duplicate Append() error = %v", err)
+	}
+
+	if len(exec.calls) != 1 {
+		t.Fatalf("exec calls = %d, want 1", len(exec.calls))
+	}
+}
+
+func TestWriterKeepsOnlyLatestDateInMileageCache(t *testing.T) {
+	exec := &recordingExec{}
+	writer := NewWriter(exec, time.FixedZone("Asia/Shanghai", 8*3600))
+	event := envelope.FrameEnvelope{
+		Protocol: envelope.ProtocolJT808,
+		VIN:      "LNBVIN00000000001",
+		Fields: map[string]any{
+			envelope.FieldTotalMileageKM: 10241.2,
+		},
+	}
+
+	event.EventTimeMS = time.Date(2026, 7, 1, 23, 59, 0, 0, time.FixedZone("Asia/Shanghai", 8*3600)).UnixMilli()
+	if err := writer.Append(context.Background(), event); err != nil {
+		t.Fatalf("first Append() error = %v", err)
+	}
+	event.EventTimeMS = time.Date(2026, 7, 2, 0, 1, 0, 0, time.FixedZone("Asia/Shanghai", 8*3600)).UnixMilli()
+	if err := writer.Append(context.Background(), event); err != nil {
+		t.Fatalf("next-day Append() error = %v", err)
+	}
+
+	if len(exec.calls) != 2 {
+		t.Fatalf("exec calls = %d, want 2", len(exec.calls))
+	}
+	if len(writer.lastTotalMileage) != 1 {
+		t.Fatalf("cache entries = %d, want 1", len(writer.lastTotalMileage))
+	}
+}
+
 type execCall struct {
 	query string
 	args  []any