DeepSeek feat: extract performance monitoring into an opt-in tool and improve error handling in teacher routes

tools/performance.ts

@@ -1,61 +1,131 @@
-import { performance } from "node:perf_hooks";
+/**
+ * Opt-in performance harness. Nothing in src/ imports this file, so the app
+ * runs without it. Load it with `yarn perf` (or `node --import ./tools/perf-hooks.mjs`).
+ */
+import mongoose from "mongoose";
+import { monitorEventLoopDelay, performance } from "node:perf_hooks";
+import express from "express";
 
-type DbMetric = {
+type Metric = {
   count: number;
   totalMs: number;
   maxMs: number;
   over100Ms: number;
 };
 
-const metrics = new Map<string, DbMetric>();
+type RequestMetric = {
+  count: number;
+  totalMs: number;
+  maxMs: number;
+  over500Ms: number;
+};
 
-export async function measureDb<T>(
-  label: string,
-  operation: () => Promise<T>,
-): Promise<T> {
-  const started = performance.now();
+const dbMetrics = new Map<string, Metric>();
+const requestMetrics = new Map<string, RequestMetric>();
 
-  try {
-    return await operation();
-  } finally {
-    const durationMs = performance.now() - started;
+const eventLoop = monitorEventLoopDelay({ resolution: 20 });
+eventLoop.enable();
 
-    let metric = metrics.get(label);
-    if (!metric) {
-      metric = { count: 0, totalMs: 0, maxMs: 0, over100Ms: 0 };
-      metrics.set(label, metric);
-    }
+// --- Database timings -------------------------------------------------------
+// Mongoose emits these for every query, so no route code has to be touched.
+export function register() {
+  mongoose.connection.on('connected', () => {
+  const client = mongoose.connection.getClient();
 
-    metric.count++;
-    metric.totalMs += durationMs;
-    metric.maxMs = Math.max(metric.maxMs, durationMs);
+  client.on('commandStarted', (event: any) => {
+    (event as any).__startedAt = performance.now();
+  });
 
-    if (durationMs > 100) {
-      metric.over100Ms++;
-    }
-  }
+  client.on('commandSucceeded', (event: any) => {
+    recordDb(`${event.commandName}.${Object.keys(event.command ?? {})[0] ?? 'unknown'}`, event);
+  });
+
+  client.on('commandFailed', (event: any) => {
+    recordDb(`${event.commandName}.failed`, event);
+  });
+  });
 }
 
-setInterval(() => {
-  if (metrics.size === 0) return;
+function recordDb(label: string, event: any) {
+  const startedAt = event.__startedAt;
+  if (typeof startedAt !== 'number') return;
 
-  const operations = Object.fromEntries(
-    [...metrics.entries()].map(([label, metric]) => [
-      label,
+  const durationMs = performance.now() - startedAt;
+
+  let metric = dbMetrics.get(label);
+  if (!metric) {
+    metric = { count: 0, totalMs: 0, maxMs: 0, over100Ms: 0 };
+    dbMetrics.set(label, metric);
+  }
+
+  metric.count++;
+  metric.totalMs += durationMs;
+  metric.maxMs = Math.max(metric.maxMs, durationMs);
+  if (durationMs > 100) metric.over100Ms++;
+}
+
+// --- Request timings --------------------------------------------------------
+// Installed by patching express.json() from the loader, so index.ts stays clean.
+export function requestTimer() {
+  const originalJson = express.json.bind(express);
+
+  express.json = ((...args: any[]) => {
+    const parser = (originalJson as any)(...args);
+    return (req: any, res: any, next: any) => {
+      const started = performance.now();
+
+      res.on("finish", () => {
+        const durationMs = performance.now() - started;
+        const key = `${req.method} ${req.route?.path ?? req.path} ${res.statusCode}`;
+
+        let metric = requestMetrics.get(key);
+        if (!metric) {
+          metric = { count: 0, totalMs: 0, maxMs: 0, over500Ms: 0 };
+          requestMetrics.set(key, metric);
+        }
+        const current = metric;
+
+        current.count++;
+        current.totalMs += durationMs;
+        current.maxMs = Math.max(current.maxMs, durationMs);
+        if (durationMs > 500) current.over500Ms++;
+      });
+
+      parser(req, res, next);
+    };
+  }) as typeof express.json;
+}
+
+// --- Reporting --------------------------------------------------------------
+function summarize<T extends { count: number; totalMs: number; maxMs: number }>(entries: [string, T][]) {
+  return Object.fromEntries(
+    entries.map(([key, value]) => [
+      key,
       {
-        count: metric.count,
-        avgMs: Number((metric.totalMs / metric.count).toFixed(2)),
-        maxMs: Number(metric.maxMs.toFixed(2)),
-        over100Ms: metric.over100Ms,
+        count: value.count,
+        avgMs: Number((value.totalMs / value.count).toFixed(2)),
+        maxMs: Number(value.maxMs.toFixed(2)),
       },
     ]),
   );
+}
+
+setInterval(() => {
+  if (requestMetrics.size === 0 && dbMetrics.size === 0) return;
 
   console.log(JSON.stringify({
-    type: "database_performance",
+    type: "performance_summary",
     timestamp: new Date().toISOString(),
-    operations,
+    requests: summarize([...requestMetrics.entries()]),
+    database: summarize([...dbMetrics.entries()]),
+    eventLoopDelayMs: {
+      mean: Number((eventLoop.mean / 1e6 || 0).toFixed(2)),
+      p95: Number((eventLoop.percentile(95) / 1e6).toFixed(2)),
+      max: Number((eventLoop.max / 1e6).toFixed(2)),
+    },
   }));
 
-  metrics.clear();
+  requestMetrics.clear();
+  dbMetrics.clear();
+  eventLoop.reset();
 }, 10_000).unref();