feat: implement GC metrics collection without native(C++) modules (#274)

* feat: implement GC metrics collection without native(C++) modules

* fix: replace summury with histogram.
Make metric names compatible with promtool check

* fix: remove duplicate metrics, update CHANGELOG.md

* Update example/server.js

Co-Authored-By: Sam Roberts <vieuxtech@gmail.com>

* Update CHANGELOG.md

Co-Authored-By: Sam Roberts <vieuxtech@gmail.com>

* fix: update README

Co-authored-by: Sam Roberts <vieuxtech@gmail.com>

CHANGELOG.md

@@ -27,6 +27,8 @@ project adheres to [Semantic Versioning](http://semver.org/).
 
 ### Added
 
+- feat: implement GC metrics collection without native(C++) modules.
+
 ## [11.5.3] - 2019-06-27
 
 ### Changed

README.md

@@ -48,13 +48,15 @@ NOTE: Some of the metrics, concerning File Descriptors and Memory, are only
 available on Linux.
 
 In addition, some Node-specific metrics are included, such as event loop lag,
-active handles and Node.js version. See what metrics there are in
+active handles, GC and Node.js version. See what metrics there are in
 [lib/metrics](lib/metrics).
 
-`collectDefaultMetrics` takes 1 options object with 3 entries, a timeout for how
-often the probe should be fired, an optional prefix for metric names
-and a registry to which metrics should be registered. By default probes are
-launched every 10 seconds, but this can be modified like this:
+`collectDefaultMetrics` takes 1 options object with up to 4 entries, a timeout for how
+often the probe should be fired, an optional prefix for metric names,
+a registry to which metrics should be registered and
+`gcDurationBuckets` with custom buckets for GC duration histogram.
+Default buckets of GC duration histogram are `[0.001, 0.01, 0.1, 1, 2, 5]` (in seconds).
+By default probes are launched every 10 seconds, but this can be modified like this:
 
 ```js
 const client = require('prom-client');
@@ -77,6 +79,16 @@ const register = new Registry();
 collectDefaultMetrics({ register });
 ```
 
+To use custom buckets for GC duration histogram, pass it in as `gcDurationBuckets`:
+
+```js
+const client = require('prom-client');
+
+const collectDefaultMetrics = client.collectDefaultMetrics;
+
+collectDefaultMetrics({ gcDurationBuckets: [0.1, 0.2, 0.3] });
+```
+
 To prefix metric names with your own arbitrary string, pass in a `prefix`:
 
 ```js

example/server.js

@@ -56,6 +56,19 @@ if (cluster.isWorker) {
 	}, 2000);
 }
 
+// Generate some garbage
+const t = [];
+setInterval(() => {
+	for (let i = 0; i < 100; i++) {
+		t.push(new Date());
+	}
+}, 10);
+setInterval(() => {
+	while (t.length > 0) {
+		t.pop();
+	}
+});
+
 server.get('/metrics', (req, res) => {
 	res.set('Content-Type', register.contentType);
 	res.end(register.metrics());
@@ -67,7 +80,10 @@ server.get('/metrics/counter', (req, res) => {
 });
 
 //Enable collection of default metrics
-require('../').collectDefaultMetrics();
+require('../').collectDefaultMetrics({
+	timeout: 10000,
+	gcDurationBuckets: [0.001, 0.01, 0.1, 1, 2, 5] // These are the default buckets.
+});
 
 console.log('Server listening to 3000, metrics exposed on /metrics endpoint');
 server.listen(3000);

index.d.ts

@@ -650,6 +650,7 @@ export interface DefaultMetricsCollectorConfiguration {
 	timestamps?: boolean;
 	register?: Registry;
 	prefix?: string;
+	gcDurationBuckets?: number[];
 }
 
 /**

lib/defaultMetrics.js

@@ -11,6 +11,7 @@ const processRequests = require('./metrics/processRequests');
 const heapSizeAndUsed = require('./metrics/heapSizeAndUsed');
 const heapSpacesSizeAndUsed = require('./metrics/heapSpacesSizeAndUsed');
 const version = require('./metrics/version');
+const gc = require('./metrics/gc');
 const { globalRegistry } = require('./registry');
 const { printDeprecationCollectDefaultMetricsNumber } = require('./util');
 
@@ -25,7 +26,8 @@ const metrics = {
 	processRequests,
 	heapSizeAndUsed,
 	heapSpacesSizeAndUsed,
-	version
+	version,
+	gc
 };
 const metricsList = Object.keys(metrics);
 

lib/metrics/gc.js

@@ -0,0 +1,54 @@
+'use strict';
+const Histogram = require('../histogram');
+
+let perf_hooks;
+
+try {
+	// eslint-disable-next-line
+	perf_hooks = require('perf_hooks');
+} catch (e) {
+	// node version is too old
+}
+
+const NODEJS_GC_DURATION_SECONDS = 'nodejs_gc_duration_seconds';
+const DEFAULT_GC_DURATION_BUCKETS = [0.001, 0.01, 0.1, 1, 2, 5];
+
+const kinds = [];
+kinds[perf_hooks.constants.NODE_PERFORMANCE_GC_MAJOR] = 'major';
+kinds[perf_hooks.constants.NODE_PERFORMANCE_GC_MINOR] = 'minor';
+kinds[perf_hooks.constants.NODE_PERFORMANCE_GC_INCREMENTAL] = 'incremental';
+kinds[perf_hooks.constants.NODE_PERFORMANCE_GC_WEAKCB] = 'weakcb';
+
+module.exports = (registry, config = {}) => {
+	if (!perf_hooks) {
+		return () => {};
+	}
+
+	const namePrefix = config.prefix ? config.prefix : '';
+	const buckets = config.gcDurationBuckets
+		? config.gcDurationBuckets
+		: DEFAULT_GC_DURATION_BUCKETS;
+	const gcHistogram = new Histogram({
+		name: namePrefix + NODEJS_GC_DURATION_SECONDS,
+		help:
+			'Garbage collection duration by kind, one of major, minor, incremental or weakcb.',
+		labelNames: ['kind'],
+		buckets,
+		registers: registry ? [registry] : undefined
+	});
+
+	const obs = new perf_hooks.PerformanceObserver(list => {
+		const entry = list.getEntries()[0];
+		const labels = { kind: kinds[entry.kind] };
+
+		// Convert duration from milliseconds to seconds
+		gcHistogram.observe(labels, entry.duration / 1000);
+	});
+
+	// We do not expect too many gc events per second, so we do not use buffering
+	obs.observe({ entryTypes: ['gc'], buffered: false });
+
+	return () => {};
+};
+
+module.exports.metricNames = [NODEJS_GC_DURATION_SECONDS];

test/metrics/gcTest.js

@@ -0,0 +1,43 @@
+'use strict';
+
+describe('gc', () => {
+	const register = require('../../index').register;
+	const processHandles = require('../../lib/metrics/gc');
+
+	beforeAll(() => {
+		register.clear();
+	});
+
+	afterEach(() => {
+		register.clear();
+	});
+
+	it('should add metric to the registry', () => {
+		expect(register.getMetricsAsJSON()).toHaveLength(0);
+
+		processHandles()();
+
+		const metrics = register.getMetricsAsJSON();
+
+		// Check if perf_hooks module is available
+		let perf_hooks;
+		try {
+			// eslint-disable-next-line
+			perf_hooks = require('perf_hooks');
+		} catch (e) {
+			// node version is too old
+		}
+
+		if (perf_hooks) {
+			expect(metrics).toHaveLength(1);
+
+			expect(metrics[0].help).toEqual(
+				'Garbage collection duration by kind, one of major, minor, incremental or weakcb.'
+			);
+			expect(metrics[0].type).toEqual('histogram');
+			expect(metrics[0].name).toEqual('nodejs_gc_duration_seconds');
+		} else {
+			expect(metrics).toHaveLength(0);
+		}
+	});
+});