fs: Change default WriteStream config, increase perf

This increases fs.WriteStream throughput dramatically by removing the
"higher default water marks" for fs.WriteStream.

Also includes a benchmark.  Current performance is significantly higher
than v0.8 for strings at all tested levels except size=1.  Buffer
performance is still lackluster.

Further improvement in the stream.Writable base class is required, but
this is a start.

benchmark/fs-write-stream-throughput.js

@@ -0,0 +1,96 @@
+
+// If there are no args, then this is the root.  Run all the benchmarks!
+if (!process.argv[2])
+  parent();
+else
+  runTest(+process.argv[2], +process.argv[3], process.argv[4]);
+
+function parent() {
+  var types = [ 'string', 'buffer' ];
+  var durs = [ 1, 5 ];
+  var sizes = [ 1, 10, 100, 2048, 10240 ];
+  var queue = [];
+  types.forEach(function(t) {
+    durs.forEach(function(d) {
+      sizes.forEach(function(s) {
+        queue.push([__filename, d, s, t]);
+      });
+    });
+  });
+
+  var spawn = require('child_process').spawn;
+  var node = process.execPath;
+
+  run();
+
+  function run() {
+    var args = queue.shift();
+    if (!args)
+      return;
+    var child = spawn(node, args, { stdio: 'inherit' });
+    child.on('close', function(code, signal) {
+      if (code)
+        throw new Error('Benchmark failed: ' + args.slice(1));
+      run();
+    });
+  }
+}
+
+function runTest(dur, size, type) {
+  if (type !== 'string')
+    type = 'buffer';
+  switch (type) {
+    case 'string':
+      var chunk = new Array(size + 1).join('a');
+      break;
+    case 'buffer':
+      var chunk = new Buffer(size);
+      chunk.fill('a');
+      break;
+  }
+
+  var writes = 0;
+  var fs = require('fs');
+  try { fs.unlinkSync('write_stream_throughput'); } catch (e) {}
+
+  var start
+  var end;
+  function done() {
+    var time = end[0] + end[1]/1E9;
+    var written = fs.statSync('write_stream_throughput').size / 1024;
+    var rate = (written / time).toFixed(2);
+    console.log('fs_write_stream_dur_%d_size_%d_type_%s: %d',
+                dur, size, type, rate);
+
+    try { fs.unlinkSync('write_stream_throughput'); } catch (e) {}
+  }
+
+  var f = require('fs').createWriteStream('write_stream_throughput');
+  f.on('drain', write);
+  f.on('open', write);
+  f.on('close', done);
+
+  // streams2 fs.WriteStreams will let you send a lot of writes into the
+  // buffer before returning false, so capture the *actual* end time when
+  // all the bytes have been written to the disk, indicated by 'finish'
+  f.on('finish', function() {
+    end = process.hrtime(start);
+  });
+
+  var ending = false;
+  function write() {
+    // don't try to write after we end, even if a 'drain' event comes.
+    // v0.8 streams are so sloppy!
+    if (ending)
+      return;
+
+    start = start || process.hrtime();
+    while (false !== f.write(chunk));
+    end = process.hrtime(start);
+
+    if (end[0] >= dur) {
+      ending = true;
+      f.end();
+    }
+  }
+}

lib/fs.js

@@ -1559,11 +1559,7 @@ function WriteStream(path, options) {
   if (!(this instanceof WriteStream))
     return new WriteStream(path, options);
 
-  // a little bit bigger buffer and water marks by default
-  options = util._extend({
-    lowWaterMark: 16 * 1024,
-    highWaterMark: 64 * 1024
-  }, options || {});
+  options = options || {};
 
   Writable.call(this, options);