fs.promises.readFile is 40% slower than fs.readFile #37583
Description
- Version: 15.10.0
- Platform: macOS
- Subsystem: 11.2.1
What steps will reproduce the bug?
Run this benchmark on a 1 MB file (big.file):
const Benchmark = require("benchmark");
const fs = require("fs");
const path = require("path");
const chalk = require("chalk");
const util = require("util");
const promisifed = util.promisify(fs.readFile);
const bigFilepath = path.resolve(__dirname, "./big.file");
const suite = new Benchmark.Suite("fs");
suite
.add(
"fs.readFileSync",
(defer) => {
fs.readFileSync(bigFilepath, "utf8");
defer.resolve();
},
{ defer: true }
)
.add(
"fs.readFile",
(defer) => {
fs.readFile(bigFilepath, (err, data) => {
defer.resolve();
});
},
{ defer: true }
)
.add(
"fs.promises.readFile",
(defer) => {
fs.promises.readFile(bigFilepath).then(() => {
defer.resolve();
});
},
{ defer: true }
)
.add(
"util.promisify(fs.readFile)",
(defer) => {
promisifed(bigFilepath).then(() => {
defer.resolve();
});
},
{ defer: true }
)
.on("cycle", function (event) {
console.log(String(event.target));
})
.on("complete", function () {
console.log(
"Fastest is " + chalk.green(this.filter("fastest").map("name"))
);
console.log("Slowest is " + chalk.red(this.filter("slowest").map("name")));
})
.run({ defer: true });To create a 1 MB file (~40% slower):
dd if=/dev/zero of=big.file count=1024 bs=1024To create a 20 KB file (~55% slower):
dd if=/dev/zero of=big.file count=20 bs=1024How often does it reproduce? Is there a required condition?
Always.
What is the expected behavior?
fs.promises.readFile should perform similarly to fs.readFile
What do you see instead?
Additional information
I suspect the cause is right here: https://github.com/nodejs/node/blob/master/lib/internal/fs/promises.js#L319-L339
Instead of creating a new Buffer for each chunk, it could allocate a single Buffer and write to that buffer. I don't think Buffer.concat or temporary arrays are necessary.