Missing caching for leaderboard API causes high database load Team: T134

.env.example

@@ -33,17 +33,6 @@ DAILY_EVALUATION_TIME=0 1 * * *
 # Use '*' for development, specify frontend URL for production
 CORS_ORIGIN=*
 
-# Email Configuration
-# SMTP settings for sending emails
-EMAIL_ENABLED=true
-SMTP_HOST=smtp.gmail.com
-SMTP_PORT=587
-SMTP_USER=padmanimayank12@gmail.com
-SMTP_PASS=mztu mhzs hhbw qbcc
-EMAIL_FROM="Code Duel <noreply@codeduel.com>"
-
-# Email Reminder Cron Configuration
-# Daily reminder time (default: 6 PM daily)
-DAILY_REMINDER_TIME=0 18 * * *
-# Weekly summary time (default: Sunday 10 AM)
-WEEKLY_SUMMARY_TIME=0 10 * * 0
+# Redis Configuration (optional - used for leaderboard caching)
+# If Redis is unavailable, the app falls back to direct database queries
+REDIS_URL=redis://localhost:6379

package.json

@@ -20,22 +20,16 @@
   "license": "ISC",
   "dependencies": {
     "@prisma/client": "^5.8.0",
-    "@prisma/client": "^5.22.0",
     "axios": "^1.6.5",
     "bcryptjs": "^2.4.3",
     "cors": "^2.8.5",
     "dotenv": "^16.3.1",
     "express": "^4.18.2",
     "express-validator": "^7.0.1",
+    "ioredis": "^5.9.3",
     "jsonwebtoken": "^9.0.2",
     "node-cron": "^3.0.3",
-    "nodemailer": "^8.0.1",
     "prisma": "^5.8.0",
-    "express-rate-limit": "^8.2.1",
-    "express-validator": "^7.3.1",
-    "jsonwebtoken": "^9.0.2",
-    "node-cron": "^3.0.3",
-    "prisma": "^5.22.0",
     "winston": "^3.11.0"
   },
   "devDependencies": {

src/config/env.js

@@ -46,6 +46,9 @@ const config = {
 
   // CORS Configuration
   corsOrigin: process.env.CORS_ORIGIN || "*",
+
+  // Redis Configuration
+  redisUrl: process.env.REDIS_URL || "redis://localhost:6379",
 };
 
 // Validate critical environment variables

src/config/redis.js

@@ -0,0 +1,86 @@
+const Redis = require("ioredis");
+const { config } = require("./env");
+const logger = require("../utils/logger");
+
+let redisClient = null;
+let isConnected = false;
+
+/**
+ * Create and configure Redis client with error handling.
+ * If Redis is unavailable, the app continues to work without caching.
+ */
+const createRedisClient = () => {
+  try {
+    redisClient = new Redis(config.redisUrl, {
+      maxRetriesPerRequest: 1,
+      retryStrategy(times) {
+        if (times > 3) {
+          logger.warn("Redis: max reconnection attempts reached, giving up");
+          return null; // Stop retrying
+        }
+        return Math.min(times * 500, 2000);
+      },
+      lazyConnect: true,
+    });
+
+    redisClient.on("connect", () => {
+      isConnected = true;
+      logger.info("Redis: connected successfully");
+    });
+
+    redisClient.on("error", (err) => {
+      isConnected = false;
+      logger.warn(`Redis: connection error - ${err.message}`);
+    });
+
+    redisClient.on("close", () => {
+      isConnected = false;
+      logger.info("Redis: connection closed");
+    });
+
+    // Attempt to connect (non-blocking)
+    redisClient.connect().catch((err) => {
+      isConnected = false;
+      logger.warn(`Redis: initial connection failed - ${err.message}. Falling back to database queries.`);
+    });
+  } catch (err) {
+    logger.warn(`Redis: failed to create client - ${err.message}. Caching disabled.`);
+    redisClient = null;
+    isConnected = false;
+  }
+};
+
+/**
+ * Check if Redis is ready to accept commands
+ * @returns {boolean}
+ */
+const isRedisReady = () => {
+  return redisClient !== null && isConnected;
+};
+
+/**
+ * Get the Redis client instance
+ * @returns {Redis|null}
+ */
+const getRedisClient = () => {
+  return redisClient;
+};
+
+/**
+ * Gracefully disconnect Redis
+ */
+const disconnectRedis = async () => {
+  if (redisClient) {
+    try {
+      await redisClient.quit();
+      logger.info("Redis: disconnected gracefully");
+    } catch (err) {
+      logger.warn(`Redis: error during disconnect - ${err.message}`);
+    }
+  }
+};
+
+// Initialize on module load
+createRedisClient();
+
+module.exports = { getRedisClient, isRedisReady, disconnectRedis };

src/controllers/dashboard.controller.js

@@ -3,6 +3,7 @@ const evaluationService = require("../services/evaluation.service");
 const penaltyService = require("../services/penalty.service");
 const statsService = require("../services/stats.service");
 const { asyncHandler } = require("../middlewares/error.middleware");
+const { getLeaderboardCache, setLeaderboardCache } = require("../services/cache.service");
 
 /**
  * Get dashboard overview for current user
@@ -64,10 +65,10 @@ const getDashboard = asyncHandler(async (req, res) => {
         totalPenalties: membership.totalPenalties,
         todayStatus: todayResult
           ? {
-              completed: todayResult.completed,
-              submissionsCount: todayResult.submissionsCount,
-              evaluatedAt: todayResult.evaluatedAt,
-            }
+            completed: todayResult.completed,
+            submissionsCount: todayResult.submissionsCount,
+            evaluatedAt: todayResult.evaluatedAt,
+          }
           : null,
         recentResults: recentResults.map((r) => ({
           date: r.date,
@@ -166,7 +167,16 @@ const getChallengeProgress = asyncHandler(async (req, res) => {
 const getChallengeLeaderboard = asyncHandler(async (req, res) => {
   const { challengeId } = req.params;
 
-  // Get all members with their stats
+  // Check cache first
+  const cachedData = await getLeaderboardCache(challengeId);
+  if (cachedData) {
+    return res.status(200).json({
+      success: true,
+      data: cachedData,
+    });
+  }
+
+  // Cache miss — query database (original logic unchanged)
   const members = await prisma.challengeMember.findMany({
     where: {
       challengeId,
@@ -212,6 +222,9 @@ const getChallengeLeaderboard = asyncHandler(async (req, res) => {
     })
   );
 
+  // Store in cache (fire-and-forget, errors handled internally)
+  await setLeaderboardCache(challengeId, leaderboard);
+
   res.status(200).json({
     success: true,
     data: leaderboard,
@@ -266,11 +279,11 @@ const getTodayStatus = asyncHandler(async (req, res) => {
         requiredSubmissions: membership.challenge.minSubmissionsPerDay,
         status: result
           ? {
-              completed: result.completed,
-              submissionsCount: result.submissionsCount,
-              problemsSolved: result.problemsSolved,
-              evaluatedAt: result.evaluatedAt,
-            }
+            completed: result.completed,
+            submissionsCount: result.submissionsCount,
+            problemsSolved: result.problemsSolved,
+            evaluatedAt: result.evaluatedAt,
+          }
           : null,
       };
     })