Performance Diagnostics

import { performance } from "node:perf_hooks";
const t0 = performance.now();
let s = 0;
for (let i = 0; i < 1000; i++) s += i;
const ms = performance.now() - t0;
ms >= 0  // true
s        // 499500

import { createHistogram } from "node:perf_hooks";
const h = createHistogram();
h.record(10);
h.record(20);
h.min  // 10
h.max  // 20

const { rss, heapUsed } = process.memoryUsage();
rss > 0       // true
heapUsed > 0  // true

// node --cpu-prof app.js
// node --heap-prof app.js
const flags = ["--cpu-prof", "--heap-prof"];
flags[0]  // "--cpu-prof"

// Bad in servers: readFileSync
// Good: await readFile(...)
import { readFile } from "node:fs/promises";
typeof readFile  // "function"

import { performance } from "node:perf_hooks";
performance.mark("a-start");
performance.mark("a-end");
performance.measure("a", "a-start", "a-end");
const entries = performance.getEntriesByName("a");
entries[0].duration >= 0  // true

import { monitorEventLoopDelay } from "node:perf_hooks";
const h = monitorEventLoopDelay({ resolution: 20 });
h.enable();
await new Promise((r) => setTimeout(r, 50));
h.disable();
h.mean >= 0  // true (nanoseconds)

const data = JSON.parse('{"n":1}');
data.n  // 1
// fine for small/medium payloads

const pool = Buffer.alloc(64 * 1024);
pool.length  // 65536

// Prefer keep-alive fetch/http agents for many calls to same host
const keepAlive = true;
keepAlive  // true

// clinic doctor -- node app.js
const tip = "clinic doctor -- node app.js";
tip.startsWith("clinic")  // true

// node --expose-gc
// global.gc?.();
typeof (global as any).gc  // "undefined" unless --expose-gc

import { Readable } from "node:stream";
const body = Readable.from(["chunk"]);
const parts: string[] = [];
for await (const c of body) parts.push(String(c));
parts  // ["chunk"]

const ids = [1, 2, 3];
// await db.query("select * from t where id = any($1)", [ids]);
ids.length  // 3

// Use autocannon/wrk against the real HTTP handler, not only a tight loop.
const tool = "autocannon";
tool.length  // 10