stream: amortize writable buffer compaction

Signed-off-by: Gürgün Dayıoğlu <hey@gurgun.day>
Assisted-by: Codex
PR-URL: #65847
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Robert Nagy <ronagy@icloud.com>
Reviewed-By: Xuguang Mei <meixuguang@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: gurgunday

benchmark/streams/writable-buffered-drain.js

@@ -0,0 +1,25 @@
+'use strict';
+
+const common = require('../common');
+const { Writable } = require('stream');
+
+const bench = common.createBenchmark(main, {
+  count: [1024, 16384, 65536],
+  n: [100],
+});
+
+function main({ count, n }) {
+  const chunk = {};
+  let callback;
+  const stream = new Writable({
+    objectMode: true,
+    write(chunk, encoding, cb) { callback = cb; },
+  });
+
+  bench.start();
+  for (let i = 0; i < n; i++) {
+    for (let j = 0; j < count; j++) stream.write(chunk);
+    for (let j = 0; j < count; j++) callback();
+  }
+  bench.end(n);
+}

lib/internal/streams/writable.js

@@ -787,7 +787,7 @@ function clearBuffer(stream, state) {
 
     if (i === buffered.length) {
       resetBuffer(state);
-    } else if (i > 256) {
+    } else if (i > 256 && i * 2 >= buffered.length) {
       buffered.splice(0, i);
       state.bufferedIndex = 0;
     } else {