perf(histogram): render the export list straight from the store iterator

CHANGELOG.md

@@ -12,6 +12,7 @@ project adheres to [Semantic Versioning](http://semver.org/).
 ### Changed
 
 - Organized default metrics
+- perf: Histogram rendering builds its export list straight from the store iterator instead of an intermediate array. Faster at high series counts on Node 24 and 26, can be slightly slower on Node 22
 
 ### Added
 

benchmarks/histogram.js

@@ -14,7 +14,11 @@
 
 'use strict';
 
-const { getLabelNames, labelCombinationFactory } = require('./utils/labels');
+const {
+	getLabelNames,
+	getLabelCombinations,
+	labelCombinationFactory,
+} = require('./utils/labels');
 
 module.exports = setupHistogramSuite;
 
@@ -100,6 +104,19 @@ function setupHistogramSuite(suite) {
 		),
 		{ teardown, setup: setup(6) },
 	);
+
+	// `method` repeats `delete`, so `1 x 64` stores 63 label sets and `2 x 8` stores 56.
+	[
+		{ name: 'no labels', counts: [] },
+		{ name: '1 x 64', counts: [64] },
+		{ name: '2 x 8', counts: [8, 8] },
+		{ name: '6 x 2', counts: [2, 2, 2, 2, 2, 2] },
+	].forEach(({ name, counts }) => {
+		suite.add(`get() ${name}`, (client, { histogram }) => histogram.get(), {
+			teardown,
+			setup: observed(counts),
+		});
+	});
 }
 
 function setup(labelCount) {
@@ -117,6 +134,25 @@ function setup(labelCount) {
 	};
 }
 
+function observed(labelCounts) {
+	return client => {
+		const registry = new client.Registry();
+
+		const histogram = new client.Histogram({
+			name: 'histogram',
+			help: 'histogram',
+			labelNames: getLabelNames(labelCounts.length),
+			registers: [registry],
+		});
+
+		getLabelCombinations(labelCounts).forEach(labels =>
+			histogram.observe({ ...labels }, 1),
+		);
+
+		return { registry, histogram };
+	};
+}
+
 function teardown(client, { registry }) {
 	registry.clear();
 }

lib/histogram.js

@@ -120,8 +120,8 @@ class Histogram extends Metric {
 			const v = this.collect();
 			if (v instanceof Promise) await v;
 		}
-		const data = Array.from(this.store.values());
-		const values = data
+		const values = this.store
+			.values()
 			.map(extractBucketValuesForExport(this))
 			.reduce(addSumAndCountForExport(this), []);