gc.js

// Copyright The Prometheus Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0

// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

'use strict';
const { debuglog } = require('node:util');
const Histogram = require('../histogram');

const debug = debuglog('prom:metrics:gc');

let perf_hooks;

try {
	perf_hooks = require('perf_hooks');
} catch (error) {
	debug('perf_hooks module is unavailable: %o', error);
}

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 = [];

if (perf_hooks !== undefined && perf_hooks.constants !== undefined) {
	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 === undefined) {
		return;
	}

	const namePrefix = config.prefix ?? '';
	const labels = config.labels ?? {};
	const labelNames = Object.keys(labels);
	const buckets = 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', ...labelNames],
		enableExemplars: false,
		buckets,
		registers: registry === undefined ? undefined : [registry],
	});

	const obs = new perf_hooks.PerformanceObserver(list => {
		const entry = list.getEntries()[0];
		// Node < 16 uses entry.kind
		// Node >= 16 uses entry.detail.kind
		// See: https://nodejs.org/docs/latest-v16.x/api/deprecations.html#deprecations_dep0152_extension_performanceentry_properties
		const kind = kinds[(entry.detail ?? entry).kind];
		// Convert duration from milliseconds to seconds
		gcHistogram.observe(Object.assign({ kind }, labels), entry.duration / 1000);
	});

	obs.observe({ entryTypes: ['gc'] });
};

module.exports.metricNames = [NODEJS_GC_DURATION_SECONDS];