ガベージコレクションのトレース

// script.mjs

import os from 'node:os';

let len = 1_000_000;
const entries = new Set();

function addEntry() {
  const entry = {
    timestamp: Date.now(),
    memory: os.freemem(),
    totalMemory: os.totalmem(),
    uptime: os.uptime(),
  };

  entries.add(entry);
}

function summary() {
  console.log(`Total: ${entries.size} entries`);
}

// execution
(() => {
  while (len > 0) {
    addEntry();
    process.stdout.write(`~~> ${len} entries to record\r`);
    len--;
  }

  summary();
})();

$ node --trace-gc script.mjs

[39067:0x158008000]     2297 ms: Scavenge 117.5 (135.8) -> 102.2 (135.8) MB, 0.8 / 0.0 ms  (average mu = 0.994, current mu = 0.994) allocation failure
[39067:0x158008000]     2375 ms: Scavenge 120.0 (138.3) -> 104.7 (138.3) MB, 0.9 / 0.0 ms  (average mu = 0.994, current mu = 0.994) allocation failure
[39067:0x158008000]     2453 ms: Scavenge 122.4 (140.8) -> 107.1 (140.8) MB, 0.7 / 0.0 ms  (average mu = 0.994, current mu = 0.994) allocation failure
[39067:0x158008000]     2531 ms: Scavenge 124.9 (143.3) -> 109.6 (143.3) MB, 0.7 / 0.0 ms  (average mu = 0.994, current mu = 0.994) allocation failure
[39067:0x158008000]     2610 ms: Scavenge 127.1 (145.5) -> 111.8 (145.5) MB, 0.7 / 0.0 ms  (average mu = 0.994, current mu = 0.994) allocation failure
[39067:0x158008000]     2688 ms: Scavenge 129.6 (148.0) -> 114.2 (148.0) MB, 0.8 / 0.0 ms  (average mu = 0.994, current mu = 0.994) allocation failure
[39067:0x158008000]     2766 ms: Scavenge 132.0 (150.5) -> 116.7 (150.5) MB, 1.1 / 0.0 ms  (average mu = 0.994, current mu = 0.994) allocation failure
Total: 1000000 entries

[13973:0x110008000]       44 ms: Scavenge 2.4 (3.2) -> 2.0 (4.2) MB, 0.5 / 0.0 ms  (average mu = 1.000, current mu = 1.000) allocation failure

node --trace-gc --max-old-space-size=50 script.mjs

[...]
<--- Last few GCs --->
[40928:0x148008000]      509 ms: Mark-sweep 46.8 (65.8) -> 40.6 (77.3) MB, 6.4 / 0.0 ms  (+ 1.4 ms in 11 steps since start of marking, biggest step 0.2 ms, walltime since start of marking 24 ms) (average mu = 0.977, current mu = 0.977) finalize incrementa[40928:0x148008000]      768 ms: Mark-sweep 56.3 (77.3) -> 47.1 (83.0) MB, 35.9 / 0.0 ms  (average mu = 0.927, current mu = 0.861) allocation failure scavenge might not succeed
<--- JS stacktrace --->
FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory [...]

node --trace-gc --max-old-space-size=100 script.mjs

<--- Last few GCs --->
[40977:0x128008000]     2066 ms: Mark-sweep (reduce) 99.6 (102.5) -> 99.6 (102.5) MB, 46.7 / 0.0 ms  (+ 0.0 ms in 0 steps since start of marking, biggest step 0.0 ms, walltime since start of marking 47 ms) (average mu = 0.154, current mu = 0.155) allocati[40977:0x128008000]     2123 ms: Mark-sweep (reduce) 99.6 (102.5) -> 99.6 (102.5) MB, 47.7 / 0.0 ms  (+ 0.0 ms in 0 steps since start of marking, biggest step 0.0 ms, walltime since start of marking 48 ms) (average mu = 0.165, current mu = 0.175) allocati

// script-fix.mjs
import fs from 'node:fs/promises';
import os from 'node:os';

let len = 1_000_000;
const fileName = `entries-${Date.now()}`;

async function addEntry() {
  const entry = {
    timestamp: Date.now(),
    memory: os.freemem(),
    totalMemory: os.totalmem(),
    uptime: os.uptime(),
  };
  await fs.appendFile(fileName, JSON.stringify(entry) + '\n');
}

async function summary() {
  const stats = await fs.lstat(fileName);
  console.log(`File size ${stats.size} bytes`);
}

// execution
(async () => {
  await fs.writeFile(fileName, '----START---\n');
  while (len > 0) {
    await addEntry();
    process.stdout.write(`~~> ${len} entries to record\r`);
    len--;
  }

  await summary();
})();

node --trace-gc script-fix.mjs

import v8 from 'v8';

// enabling trace-gc
v8.setFlagsFromString('--trace-gc');

// disabling trace-gc
v8.setFlagsFromString('--notrace-gc');

const { PerformanceObserver } = require('node:perf_hooks');

// Create a performance observer
const obs = new PerformanceObserver(list => {
  const entry = list.getEntries()[0];
  /*
  The entry is an instance of PerformanceEntry containing
  metrics of a single garbage collection event.
  For example:
  PerformanceEntry {
    name: 'gc',
    entryType: 'gc',
    startTime: 2820.567669,
    duration: 1.315709,
    kind: 1
  }
  */
});

// Subscribe to notifications of GCs
obs.observe({ entryTypes: ['gc'] });

// Stop subscription
obs.disconnect();

{
  "name": "gc",
  "entryType": "gc",
  "startTime": 2820.567669,
  "duration": 1.315709,
  "kind": 1
}