Cached Page

A cached page is a snapshot or stored copy of a webpage saved at a specific point in time. Search engines and browsers use caching to improve page load times, reduce server load, and provide access to content even when the original page is unavailable.

Types of Caching

1. Browser Caching

<!-- Cache Control Headers -->
<meta http-equiv="Cache-Control" content="max-age=3600, public">
<meta http-equiv="Expires" content="Thu, 31 Dec 2024 23:59:59 GMT">

<!-- ETag Implementation -->
<?php
$etag = md5_file($filename);
header('ETag: "' . $etag . '"');
?>

2. Server Caching

# Apache Cache Configuration
<IfModule mod_expires.c>
    ExpiresActive On
    ExpiresByType image/jpg "access plus 1 year"
    ExpiresByType image/jpeg "access plus 1 year"
    ExpiresByType image/png "access plus 1 year"
    ExpiresByType text/css "access plus 1 month"
    ExpiresByType text/javascript "access plus 1 month"
    ExpiresByType application/javascript "access plus 1 month"
</IfModule>

Implementation Methods

1. Cache Headers

// PHP Cache Headers
header("Cache-Control: public, max-age=31536000");
header("Expires: " . gmdate("D, d M Y H:i:s", time() + 31536000) . " GMT");
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT");

// Conditional Get
$etag = md5($content);
header("ETag: \"$etag\"");

if (isset($_SERVER['HTTP_IF_NONE_MATCH']) && trim($_SERVER['HTTP_IF_NONE_MATCH']) == "\"$etag\"") {
    header("HTTP/1.1 304 Not Modified");
    exit;
}

2. Service Worker

// Service Worker Cache
self.addEventListener('install', event => {
  event.waitUntil(
    caches.open('v1').then(cache => {
      return cache.addAll([
        '/',
        '/styles/main.css',
        '/scripts/main.js',
        '/images/logo.png'
      ]);
    })
  );
});

self.addEventListener('fetch', event => {
  event.respondWith(
    caches.match(event.request).then(response => {
      return response || fetch(event.request);
    })
  );
});

Search Engine Caching

1. Google Cache Access

<!-- Google Cache Meta Tags -->
<meta name="robots" content="max-snippet:200, max-image-preview:large">
<link rel="canonical" href="https://example.com/original-page">

<!-- Cache Control for Search Engines -->
<meta name="googlebot" content="max-snippet:-1, max-image-preview:large, max-video-preview:-1">

2. Cache Management

// Cache Purge Request
async function requestCacheUpdate(url) {
  try {
    await fetch('https://www.google.com/ping', {
      method: 'POST',
      body: JSON.stringify({
        url: url,
        type: 'URL_UPDATED'
      })
    });
    
    console.log('Cache update requested for:', url);
  } catch (error) {
    console.error('Cache update request failed:', error);
  }
}

Performance Benefits

1. Load Time Improvements

• Reduced server load
• Faster page loading
• Better user experience
• Lower bandwidth usage
• Improved performance
• Reduced latency
• Resource optimization

2. Availability Benefits

• Offline access
• Backup availability
• Server downtime protection
• Network resilience
• Content preservation
• Historical access
• Emergency fallback

Cache Control

1. Cache Headers

# Nginx Cache Configuration
location ~* \.(jpg|jpeg|png|gif|ico|css|js)$ {
    expires 1y;
    add_header Cache-Control "public, no-transform";
}

location ~* \.(html|htm)$ {
    expires 1h;
    add_header Cache-Control "public, must-revalidate";
}

2. Dynamic Cache Control

// Dynamic Cache Duration
function setCacheDuration($content_type, $update_frequency) {
    $durations = [
        'static' => 31536000,  // 1 year
        'dynamic' => 3600,     // 1 hour
        'api' => 300           // 5 minutes
    ];
    
    $max_age = $durations[$update_frequency] ?? 0;
    header("Cache-Control: public, max-age=$max_age");
}

Best Practices

1. Cache Strategy

• Resource prioritization
• Cache duration settings
• Version management
• Cache invalidation
• Update protocols
• Monitoring systems
• Performance metrics

2. Implementation Guidelines

• Proper cache headers
• Resource versioning
• Cache busting
• Browser compatibility
• Mobile optimization
• Security considerations
• Performance testing

Common Issues

1. Cache Problems

• Stale content
• Cache conflicts
• Version mismatches
• Storage limitations
• Browser inconsistencies
• Update delays
• Security concerns

2. Solutions

// Cache Busting Implementation
const cacheBuster = {
  addVersioning(url) {
    const version = this.getResourceVersion();
    return `${url}?v=${version}`;
  },
  
  getResourceVersion() {
    return process.env.BUILD_ID || Date.now();
  },
  
  clearCache() {
    if ('caches' in window) {
      caches.keys().then(cacheNames => {
        return Promise.all(
          cacheNames.map(cacheName => {
            return caches.delete(cacheName);
          })
        );
      });
    }
  }
};

Remember that effective cache management balances performance improvements with content freshness. Regular monitoring and proper cache control implementation help maintain optimal website performance while ensuring users access current content.