Merge pull request #13786 from guardian/perf-gc-report

Add a script to summarise garbage collection reports using `node --trace-gc`

Author: arelra

dotcom-rendering/scripts/perf/gc/gc-report.js

@@ -0,0 +1,75 @@
+/* eslint-disable -- perf script */
+const fs = require('node:fs');
+const readline = require('node:readline');
+
+const logFilePath = process.argv[2];
+if (!logFilePath) {
+	console.error('Usage: node gc-summary.js <trace-gc-log-file>');
+	process.exit(1);
+}
+
+// Global stats
+let totalGCCount = 0;
+let totalPauseTime = 0;
+let maxPauseTime = 0;
+
+// Per-type stats
+const gcStatsByType = {};
+
+const lineReader = readline.createInterface({
+	input: fs.createReadStream(logFilePath),
+	crlfDelay: Infinity,
+});
+
+lineReader.on('line', (line) => {
+	// Match GC type: e.g., "Scavenge", "Mark-Compact (reduce)", etc.
+	const typeMatch = line.match(/:\s*(\w+(?:-\w+)?(?:\s*\(\w+\))?)/);
+	const pauseMatch =
+		line.match(/([0-9]+\.[0-9]+)\s*\/\s*[0-9.]+\s*ms/) ||
+		line.match(/([0-9]+\.[0-9]+)\s*ms/);
+
+	if (pauseMatch && typeMatch) {
+		const pause = parseFloat(pauseMatch[1]);
+		const type = typeMatch[1].trim();
+
+		totalGCCount++;
+		totalPauseTime += pause;
+		if (pause > maxPauseTime) maxPauseTime = pause;
+
+		if (!gcStatsByType[type]) {
+			gcStatsByType[type] = {
+				count: 0,
+				totalPause: 0,
+				maxPause: 0,
+			};
+		}
+
+		gcStatsByType[type].count++;
+		gcStatsByType[type].totalPause += pause;
+		if (pause > gcStatsByType[type].maxPause) {
+			gcStatsByType[type].maxPause = pause;
+		}
+	}
+});
+
+lineReader.on('close', () => {
+	console.log(`🧹 Total GC Events: ${totalGCCount}`);
+	console.log(`⏱️ Total GC Pause Time: ${totalPauseTime.toFixed(2)} ms`);
+	console.log(
+		`📊 Average GC Pause: ${(totalGCCount
+			? totalPauseTime / totalGCCount
+			: 0
+		).toFixed(2)} ms`,
+	);
+	console.log(`🚨 Longest GC Pause: ${maxPauseTime.toFixed(2)} ms`);
+	console.log('\n📚 GC Breakdown by Type:\n');
+
+	for (const [type, stats] of Object.entries(gcStatsByType)) {
+		const avg = stats.totalPause / stats.count;
+		console.log(`👉 ${type}`);
+		console.log(`   - Count: ${stats.count}`);
+		console.log(`   - Total Pause: ${stats.totalPause.toFixed(2)} ms`);
+		console.log(`   - Average Pause: ${avg.toFixed(2)} ms`);
+		console.log(`   - Max Pause: ${stats.maxPause.toFixed(2)} ms\n`);
+	}
+});