Merge pull request #26085 from smarterclayton/delay_flush

Automatic merge from submit-queue

Delay flush if the watch queue has pending items

Simple deferral of flush can reduce Syscalls when watch queues build up.

Simpler version of #24768

Fixes #24729

@xiang90 @wojtek-t

pkg/apiserver/watch.go

@@ -203,7 +203,9 @@ func (s *WatchServer) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 				// client disconnect.
 				return
 			}
-			flusher.Flush()
+			if len(ch) == 0 {
+				flusher.Flush()
+			}
 
 			buf.Reset()
 		}