From 003f2157671a694aefecd4dbb7df786e27200a18 Mon Sep 17 00:00:00 2001
From: Wei Fu <fuweid89@gmail.com>
Date: Tue, 11 Mar 2025 13:26:55 -0400
Subject: [PATCH] *: reduce tracing events during streaming JSON objects

If apiserver is handing heavy traffic volume, it's likely to trigger
tracing events. After streaming JSON objects, the number of tracing events
are same to object number. It's unneccessary to log each write call.
This patch is to reduce tracing events.

Signed-off-by: Wei Fu <fuweid89@gmail.com>
---
 .../handlers/responsewriters/writers.go       | 48 ++++++++++++-------
 1 file changed, 30 insertions(+), 18 deletions(-)

diff --git a/staging/src/k8s.io/apiserver/pkg/endpoints/handlers/responsewriters/writers.go b/staging/src/k8s.io/apiserver/pkg/endpoints/handlers/responsewriters/writers.go
index ec5ff956320..c408c556df0 100644
--- a/staging/src/k8s.io/apiserver/pkg/endpoints/handlers/responsewriters/writers.go
+++ b/staging/src/k8s.io/apiserver/pkg/endpoints/handlers/responsewriters/writers.go
@@ -200,6 +200,10 @@ type deferredResponseWriter struct {
 	hasWritten  bool
 	hw          http.ResponseWriter
 	w           io.Writer
+	// totalBytes is the number of bytes written to `w` and does not include buffered bytes
+	totalBytes int
+	// lastWriteErr holds the error result (if any) of the last write attempt to `w`
+	lastWriteErr error
 
 	ctx context.Context
 }
@@ -242,26 +246,11 @@ func (w *deferredResponseWriter) Write(p []byte) (n int, err error) {
 }
 
 func (w *deferredResponseWriter) unbufferedWrite(p []byte) (n int, err error) {
-	ctx := w.ctx
-	span := tracing.SpanFromContext(ctx)
-	// This Step usually wraps in-memory object serialization.
-	span.AddEvent("About to start writing response", attribute.Int("size", len(p)))
-
-	firstWrite := !w.hasWritten
 	defer func() {
-		if err != nil {
-			span.AddEvent("Write call failed",
-				attribute.String("writer", fmt.Sprintf("%T", w.w)),
-				attribute.Int("size", len(p)),
-				attribute.Bool("firstWrite", firstWrite),
-				attribute.String("err", err.Error()))
-		} else {
-			span.AddEvent("Write call succeeded",
-				attribute.String("writer", fmt.Sprintf("%T", w.w)),
-				attribute.Int("size", len(p)),
-				attribute.Bool("firstWrite", firstWrite))
-		}
+		w.totalBytes += n
+		w.lastWriteErr = err
 	}()
+
 	if w.hasWritten {
 		return w.w.Write(p)
 	}
@@ -282,12 +271,35 @@ func (w *deferredResponseWriter) unbufferedWrite(p []byte) (n int, err error) {
 		w.w = hw
 	}
 
+	span := tracing.SpanFromContext(w.ctx)
+	span.AddEvent("About to start writing response",
+		attribute.String("writer", fmt.Sprintf("%T", w.w)),
+		attribute.Int("size", len(p)),
+	)
+
 	header.Set("Content-Type", w.mediaType)
 	hw.WriteHeader(w.statusCode)
 	return w.w.Write(p)
 }
 
 func (w *deferredResponseWriter) Close() (err error) {
+	defer func() {
+		if !w.hasWritten {
+			return
+		}
+
+		span := tracing.SpanFromContext(w.ctx)
+
+		if w.lastWriteErr != nil {
+			span.AddEvent("Write call failed",
+				attribute.Int("size", w.totalBytes),
+				attribute.String("err", w.lastWriteErr.Error()))
+		} else {
+			span.AddEvent("Write call succeeded",
+				attribute.Int("size", w.totalBytes))
+		}
+	}()
+
 	if !w.hasWritten {
 		if !w.hasBuffered {
 			return nil