diff --git a/go/vehicle-gateway/internal/stats/daily_metric.go b/go/vehicle-gateway/internal/stats/daily_metric.go
index 807212e7..995ec0c5 100644
--- a/go/vehicle-gateway/internal/stats/daily_metric.go
+++ b/go/vehicle-gateway/internal/stats/daily_metric.go
@@ -65,6 +65,7 @@ func (w *Writer) Append(ctx context.Context, env envelope.FrameEnvelope) error {
 			sample.TotalMileageKM); err != nil {
 			return err
 		}
+		w.markMileageWritten(sample)
 	}
 	return nil
 }
@@ -77,13 +78,20 @@ func (w *Writer) seenSameMileage(sample MetricSample) bool {
 	if last, ok := w.lastTotalMileage[key]; ok && last == sample.TotalMileageKM {
 		return true
 	}
+	return false
+}
+
+func (w *Writer) markMileageWritten(sample MetricSample) {
+	prefix := fmt.Sprintf("%s|%s|", sample.VIN, sample.Protocol)
+	key := prefix + sample.StatDate
+	w.mu.Lock()
+	defer w.mu.Unlock()
 	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) {
diff --git a/go/vehicle-gateway/internal/stats/daily_metric_test.go b/go/vehicle-gateway/internal/stats/daily_metric_test.go
index 4be39fbe..6c72e9c1 100644
--- a/go/vehicle-gateway/internal/stats/daily_metric_test.go
+++ b/go/vehicle-gateway/internal/stats/daily_metric_test.go
@@ -3,6 +3,7 @@ package stats
 import (
 	"context"
 	"database/sql"
+	"errors"
 	"strings"
 	"testing"
 	"time"
@@ -174,6 +175,30 @@ func TestWriterSkipsConsecutiveDuplicateMileageSamples(t *testing.T) {
 	}
 }
 
+func TestWriterDoesNotCacheMileageWhenUpsertFails(t *testing.T) {
+	exec := &recordingExec{errs: []error{errors.New("mysql unavailable"), nil}}
+	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 = nil, want mysql error")
+	}
+	if err := writer.Append(context.Background(), event); err != nil {
+		t.Fatalf("retry Append() error = %v", err)
+	}
+
+	if len(exec.calls) != 2 {
+		t.Fatalf("exec calls = %d, want 2", len(exec.calls))
+	}
+}
+
 func TestWriterKeepsOnlyLatestDateInMileageCache(t *testing.T) {
 	exec := &recordingExec{}
 	writer := NewWriter(exec, time.FixedZone("Asia/Shanghai", 8*3600))
@@ -209,9 +234,15 @@ type execCall struct {
 
 type recordingExec struct {
 	calls []execCall
+	errs  []error
 }
 
 func (e *recordingExec) ExecContext(_ context.Context, query string, args ...any) (sql.Result, error) {
 	e.calls = append(e.calls, execCall{query: query, args: args})
+	if len(e.errs) > 0 {
+		err := e.errs[0]
+		e.errs = e.errs[1:]
+		return nil, err
+	}
 	return nil, nil
 }