http: Don't hot-path end() for large buffers

The benefits of the hot-path optimization below start to fall off when
the buffer size gets up near 128KB, because the cost of the copy is more
than the cost of the extra write() call.  Switch to the write/end method
at that point.

Heuristics and magic numbers are awful, but slow http responses are
worse.

Fix #4975

1 files changed, 8 insertions, 0 deletions

diff --git a/lib/http.js b/lib/http.js
index 2bceaa0152..dacedd4477 100644
--- a/lib/http.js
+++ b/lib/http.js
@@ -855,6 +855,14 @@ OutgoingMessage.prototype.end = function(data, encoding) {
             this.connection.writable &&
             this.connection._httpMessage === this;
 
+  // The benefits of the hot-path optimization below start to fall
+  // off when the buffer size gets up near 128KB, because the cost
+  // of the copy is more than the cost of the extra write() call.
+  // Switch to the write/end method at that point.  Heuristics and
+  // magic numbers are awful, but slow http responses are worse.
+  if (hot && Buffer.isBuffer(data) && data.length > 120 * 1024)
+    hot = false;
+
   if (hot) {
     // Hot path. They're doing
     //   res.writeHead();