diff --git a/core/logx/rotatelogger.go b/core/logx/rotatelogger.go
index 5944d59358e3..0b8f0b1468f9 100644
--- a/core/logx/rotatelogger.go
+++ b/core/logx/rotatelogger.go
@@ -115,7 +115,9 @@ func (r *DailyRotateRule) OutdatedFiles() []string {
 
 	var buf strings.Builder
 	boundary := time.Now().Add(-time.Hour * time.Duration(hoursPerDay*r.days)).Format(dateFormat)
-	fmt.Fprintf(&buf, "%s%s%s", r.filename, r.delimiter, boundary)
+	buf.WriteString(r.filename)
+	buf.WriteString(r.delimiter)
+	buf.WriteString(boundary)
 	if r.gzip {
 		buf.WriteString(gzipExt)
 	}
diff --git a/core/stat/alert.go b/core/stat/alert.go
index db604dadff90..e53c7e3118a7 100644
--- a/core/stat/alert.go
+++ b/core/stat/alert.go
@@ -46,14 +46,14 @@ func Report(msg string) {
 	if fn != nil {
 		reported := lessExecutor.DoOrDiscard(func() {
 			var builder strings.Builder
-			fmt.Fprintf(&builder, "%s\n", time.Now().Format(timeFormat))
+			builder.WriteString(fmt.Sprintln(time.Now().Format(timeFormat)))
 			if len(clusterName) > 0 {
-				fmt.Fprintf(&builder, "cluster: %s\n", clusterName)
+				builder.WriteString(fmt.Sprintf("cluster: %s\n", clusterName))
 			}
-			fmt.Fprintf(&builder, "host: %s\n", sysx.Hostname())
+			builder.WriteString(fmt.Sprintf("host: %s\n", sysx.Hostname()))
 			dp := atomic.SwapInt32(&dropped, 0)
 			if dp > 0 {
-				fmt.Fprintf(&builder, "dropped: %d\n", dp)
+				builder.WriteString(fmt.Sprintf("dropped: %d\n", dp))
 			}
 			builder.WriteString(strings.TrimSpace(msg))
 			fn(builder.String())