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Implement Caching Strategy

Design and implement caching solutions

Instructions

  1. Caching Strategy Analysis

    • Analyze application architecture and identify caching opportunities
    • Assess current performance bottlenecks and data access patterns
    • Define caching requirements (TTL, invalidation, consistency)
    • Plan multi-layer caching architecture (browser, CDN, application, database)
    • Evaluate caching technologies and storage solutions

  2. Browser and Client-Side Caching

    • Configure HTTP caching headers and cache policies:

    HTTP Cache Headers:

    // Express.js middleware
app.use((req, res, next) => {
  // Static assets with long-term caching
  if (req.url.match(/\.(js|css|png|jpg|jpeg|gif|ico|svg)$/)) {
    res.setHeader('Cache-Control', 'public, max-age=31536000'); // 1 year
    res.setHeader('ETag', generateETag(req.url));
  }
  
  // API responses with short-term caching
  if (req.url.startsWith('/api/')) {
    res.setHeader('Cache-Control', 'public, max-age=300'); // 5 minutes
  }
  
  next();
});

    Service Worker Caching:

    // sw.js - Service Worker
const CACHE_NAME = 'app-cache-v1';
const urlsToCache = [
  '/',
  '/static/js/bundle.js',
  '/static/css/main.css',
];

self.addEventListener('install', (event) => {
  event.waitUntil(
    caches.open(CACHE_NAME)
      .then((cache) => cache.addAll(urlsToCache))
  );
});

self.addEventListener('fetch', (event) => {
  event.respondWith(
    caches.match(event.request)
      .then((response) => {
        // Return cached version or fetch from network
        return response || fetch(event.request);
      })
  );
});

  3. Application-Level Caching

    • Implement in-memory and distributed caching:

    Node.js Memory Cache:

    const NodeCache = require('node-cache');
const cache = new NodeCache({ stdTTL: 600 }); // 10 minutes default TTL

class CacheService {
  static get(key) {
    return cache.get(key);
  }

  static set(key, value, ttl = 600) {
    return cache.set(key, value, ttl);
  }

  static del(key) {
    return cache.del(key);
  }

  static flush() {
    return cache.flushAll();
  }

  // Cache wrapper for expensive operations
  static async memoize(key, fn, ttl = 600) {
    let result = this.get(key);
    if (result === undefined) {
      result = await fn();
      this.set(key, result, ttl);
    }
    return result;
  }
}

// Usage example
app.get('/api/users/:id', async (req, res) => {
  const userId = req.params.id;
  const cacheKey = `user:${userId}`;
  
  const user = await CacheService.memoize(
    cacheKey,
    () => getUserFromDatabase(userId),
    900 // 15 minutes
  );
  
  res.json(user);
});

    Redis Distributed Cache:

    const redis = require('redis');
const client = redis.createClient({
  host: process.env.REDIS_HOST || 'localhost',
  port: process.env.REDIS_PORT || 6379,
});

class RedisCache {
  static async get(key) {
    try {
      const value = await client.get(key);
      return value ? JSON.parse(value) : null;
    } catch (error) {
      console.error('Cache get error:', error);
      return null;
    }
  }

  static async set(key, value, ttl = 600) {
    try {
      const serialized = JSON.stringify(value);
      if (ttl) {
        await client.setex(key, ttl, serialized);
      } else {
        await client.set(key, serialized);
      }
      return true;
    } catch (error) {
      console.error('Cache set error:', error);
      return false;
    }
  }

  static async del(key) {
    try {
      await client.del(key);
      return true;
    } catch (error) {
      console.error('Cache delete error:', error);
      return false;
    }
  }

  // Pattern-based cache invalidation
  static async invalidatePattern(pattern) {
    try {
      const keys = await client.keys(pattern);
      if (keys.length > 0) {
        await client.del(keys);
      }
      return true;
    } catch (error) {
      console.error('Cache invalidation error:', error);
      return false;
    }
  }
}

  4. Database Query Caching

    • Implement database-level caching strategies:

    PostgreSQL Query Caching:

    const { Pool } = require('pg');
const pool = new Pool();

class DatabaseCache {
  static async cachedQuery(sql, params = [], ttl = 300) {
    const cacheKey = `query:${Buffer.from(sql + JSON.stringify(params)).toString('base64')}`;
    
    // Try cache first
    let result = await RedisCache.get(cacheKey);
    if (result) {
      return result;
    }
    
    // Execute query and cache result
    const dbResult = await pool.query(sql, params);
    result = dbResult.rows;
    
    await RedisCache.set(cacheKey, result, ttl);
    return result;
  }

  // Invalidate cache by table
  static async invalidateTable(tableName) {
    await RedisCache.invalidatePattern(`query:*${tableName}*`);
  }
}

// Usage
app.get('/api/products', async (req, res) => {
  const products = await DatabaseCache.cachedQuery(
    'SELECT * FROM products WHERE active = true ORDER BY created_at DESC',
    [],
    600 // 10 minutes
  );
  res.json(products);
});

    MongoDB Caching with Mongoose:

    const mongoose = require('mongoose');

// Mongoose query caching plugin
function cachePlugin(schema) {
  schema.add({
    cacheKey: { type: String, index: true },
    cachedAt: { type: Date },
  });

  schema.methods.cache = function(ttl = 300) {
    this.cacheKey = this.constructor.generateCacheKey(this);
    this.cachedAt = new Date();
    return this;
  };

  schema.statics.findCached = async function(query, ttl = 300) {
    const cacheKey = this.generateCacheKey(query);
    
    let result = await RedisCache.get(cacheKey);
    if (result) {
      return result;
    }
    
    result = await this.find(query);
    await RedisCache.set(cacheKey, result, ttl);
    return result;
  };

  schema.statics.generateCacheKey = function(data) {
    return `${this.modelName}:${JSON.stringify(data)}`;
  };
}

// Apply plugin to schema
const ProductSchema = new mongoose.Schema({
  name: String,
  price: Number,
  category: String,
});

ProductSchema.plugin(cachePlugin);

  5. API Response Caching

    • Implement comprehensive API caching:

    Express Cache Middleware:

    function cacheMiddleware(ttl = 300) {
  return async (req, res, next) => {
    // Only cache GET requests
    if (req.method !== 'GET') {
      return next();
    }

    const cacheKey = `api:${req.originalUrl}`;
    const cached = await RedisCache.get(cacheKey);

    if (cached) {
      return res.json(cached);
    }

    // Override res.json to cache the response
    const originalJson = res.json;
    res.json = function(data) {
      RedisCache.set(cacheKey, data, ttl);
      return originalJson.call(this, data);
    };

    next();
  };
}

// Usage
app.get('/api/dashboard', cacheMiddleware(600), async (req, res) => {
  const dashboardData = await getDashboardData();
  res.json(dashboardData);
});

    GraphQL Query Caching:

    const { ApolloServer } = require('apollo-server-express');
const { ResponseCache } = require('apollo-server-plugin-response-cache');

const server = new ApolloServer({
  typeDefs,
  resolvers,
  plugins: [
    ResponseCache({
      sessionId: (requestContext) => 
        requestContext.request.http.headers.authorization || null,
      maximumAge: 300, // 5 minutes default
      scope: 'PUBLIC',
    }),
  ],
  cacheControl: {
    defaultMaxAge: 300,
    calculateHttpHeaders: false,
    stripFormattedExtensions: false,
  },
});

// Resolver-level caching
const resolvers = {
  Query: {
    products: async (parent, args, context) => {
      return await DatabaseCache.cachedQuery(
        'SELECT * FROM products WHERE category = $1',
        [args.category],
        600
      );
    },
  },
};

  6. Cache Invalidation Strategies

    • Implement intelligent cache invalidation:

    Event-Driven Cache Invalidation:

    const EventEmitter = require('events');
const cacheInvalidator = new EventEmitter();

class CacheInvalidator {
  static invalidateUser(userId) {
    const patterns = [
      `user:${userId}*`,
      `api:/api/users/${userId}*`,
      'api:/api/dashboard*', // If dashboard shows user data
    ];
    
    patterns.forEach(async (pattern) => {
      await RedisCache.invalidatePattern(pattern);
    });
    
    cacheInvalidator.emit('user:updated', userId);
  }

  static invalidateProduct(productId) {
    const patterns = [
      `product:${productId}*`,
      'api:/api/products*',
      'query:*products*',
    ];
    
    patterns.forEach(async (pattern) => {
      await RedisCache.invalidatePattern(pattern);
    });
  }
}

// Trigger invalidation on data changes
app.put('/api/users/:id', async (req, res) => {
  const userId = req.params.id;
  await updateUser(userId, req.body);
  
  // Invalidate related caches
  CacheInvalidator.invalidateUser(userId);
  
  res.json({ success: true });
});

  7. Frontend Caching Strategies

    • Implement client-side caching:

    React Query Caching:

    import { QueryClient, QueryClientProvider, useQuery } from 'react-query';

const queryClient = new QueryClient({
  defaultOptions: {
    queries: {
      staleTime: 5 * 60 * 1000, // 5 minutes
      cacheTime: 10 * 60 * 1000, // 10 minutes
      retry: 3,
      refetchOnWindowFocus: false,
    },
  },
});

function ProductList() {
  const { data: products, isLoading, error } = useQuery(
    'products',
    () => fetch('/api/products').then(res => res.json()),
    {
      staleTime: 10 * 60 * 1000, // 10 minutes
      cacheTime: 30 * 60 * 1000, // 30 minutes
    }
  );

  if (isLoading) return <div>Loading...</div>;
  if (error) return <div>Error: {error.message}</div>;

  return (
    <div>
      {products.map(product => (
        <div key={product.id}>{product.name}</div>
      ))}
    </div>
  );
}

    Local Storage Caching:

    class LocalStorageCache {
  static set(key, value, ttl = 3600000) { // 1 hour default
    const item = {
      value,
      expiry: Date.now() + ttl,
    };
    localStorage.setItem(key, JSON.stringify(item));
  }

  static get(key) {
    const item = localStorage.getItem(key);
    if (!item) return null;

    const parsed = JSON.parse(item);
    if (Date.now() > parsed.expiry) {
      localStorage.removeItem(key);
      return null;
    }

    return parsed.value;
  }

  static remove(key) {
    localStorage.removeItem(key);
  }

  static clear() {
    localStorage.clear();
  }
}

  8. Cache Monitoring and Analytics

    • Set up cache performance monitoring:

    Cache Metrics Collection:

    class CacheMetrics {
  static hits = 0;
  static misses = 0;
  static errors = 0;

  static recordHit() {
    this.hits++;
  }

  static recordMiss() {
    this.misses++;
  }

  static recordError() {
    this.errors++;
  }

  static getStats() {
    const total = this.hits + this.misses;
    return {
      hits: this.hits,
      misses: this.misses,
      errors: this.errors,
      hitRate: total > 0 ? (this.hits / total * 100).toFixed(2) : 0,
      total,
    };
  }

  static reset() {
    this.hits = 0;
    this.misses = 0;
    this.errors = 0;
  }
}

// Enhanced cache service with metrics
class MetricsCache {
  static async get(key) {
    try {
      const value = await RedisCache.get(key);
      if (value !== null) {
        CacheMetrics.recordHit();
      } else {
        CacheMetrics.recordMiss();
      }
      return value;
    } catch (error) {
      CacheMetrics.recordError();
      throw error;
    }
  }
}

// Metrics endpoint
app.get('/api/cache/stats', (req, res) => {
  res.json(CacheMetrics.getStats());
});

  9. Cache Warming and Preloading

    • Implement cache warming strategies:

    Scheduled Cache Warming:

    const cron = require('node-cron');

class CacheWarmer {
  static async warmPopularData() {
    console.log('Starting cache warming...');
    
    // Warm popular products
    const popularProducts = await DatabaseCache.cachedQuery(
      'SELECT * FROM products ORDER BY view_count DESC LIMIT 100',
      [],
      3600 // 1 hour
    );
    
    // Warm user sessions
    const activeUsers = await DatabaseCache.cachedQuery(
      'SELECT id FROM users WHERE last_active > NOW() - INTERVAL 1 DAY',
      [],
      1800 // 30 minutes
    );
    
    console.log(`Warmed cache for ${popularProducts.length} products and ${activeUsers.length} users`);
  }

  static async warmOnDemand(cacheKeys) {
    for (const key of cacheKeys) {
      if (!(await RedisCache.get(key))) {
        // Generate cache for missing keys
        await this.generateCacheForKey(key);
      }
    }
  }
}

// Schedule cache warming
cron.schedule('0 */6 * * *', () => { // Every 6 hours
  CacheWarmer.warmPopularData();
});

  10. Testing and Validation

    • Set up cache testing and validation:

    Cache Testing:

    // tests/cache.test.js
const request = require('supertest');
const app = require('../app');

describe('Cache Performance', () => {
  test('should cache API responses', async () => {
    // First request - should miss cache
    const start1 = Date.now();
    const response1 = await request(app).get('/api/products');
    const duration1 = Date.now() - start1;

    // Second request - should hit cache
    const start2 = Date.now();
    const response2 = await request(app).get('/api/products');
    const duration2 = Date.now() - start2;

    expect(response1.body).toEqual(response2.body);
    expect(duration2).toBeLessThan(duration1 / 2); // Cached should be faster
  });

  test('should invalidate cache properly', async () => {
    // Get initial data
    const initial = await request(app).get('/api/products');
    
    // Update data
    await request(app)
      .put('/api/products/1')
      .send({ name: 'Updated Product' });
    
    // Should get updated data
    const updated = await request(app).get('/api/products');
    expect(updated.body).not.toEqual(initial.body);
  });
});