Caching strategies in Wordpress - Performance & Optimization

Performance: Caching strategies

HIGH IMPACT

Caching strategies improve page load speed by reducing server processing and network requests.

Serving dynamic WordPress pages efficiently

Wordpress

<?php
// Use page caching plugin or object cache
// Cached HTML served directly without PHP processing
?>

Serves pre-built HTML quickly without running PHP or DB queries on each request.

📈 Performance GainReduces server response time by 70-90%, improves LCP significantly

Serving dynamic WordPress pages efficiently

Wordpress

<?php
// No caching, every page loads fresh
get_header();
// heavy database queries here
get_footer();
?>

Every page request triggers full PHP execution and database queries, slowing response.

📉 Performance CostBlocks rendering for 200-500ms per request depending on server load

Performance Comparison

Pattern	DOM Operations	Reflows	Paint Cost	Verdict
No caching, full PHP load	High (dynamic DOM generation)	Multiple reflows due to slow load	High paint cost due to delayed content	[X] Bad
Page caching with static HTML	Low (static DOM)	Single reflow after fast load	Low paint cost, content appears quickly	[OK] Good
No cache headers on assets	N/A	N/A	High paint cost due to delayed asset load	[X] Bad
Cache headers with deferred scripts	N/A	N/A	Low paint cost, faster asset load	[OK] Good

Rendering Pipeline

Caching reduces server processing and network delays, allowing the browser to start rendering faster.

→Network

→Server Processing

→Style Calculation

→Layout

⚠️ BottleneckServer Processing and Network Latency

Core Web Vital Affected

LCP

Caching strategies improve page load speed by reducing server processing and network requests.

Optimization Tips

1Always use page caching to serve static HTML for dynamic WordPress pages.

2Set proper cache-control headers on static assets to enable browser caching.

3Defer non-critical JavaScript to avoid blocking rendering and improve load speed.

Performance Quiz - 3 Questions

Which caching strategy most improves Largest Contentful Paint (LCP) in WordPress?

A Disabling all caching to always load fresh content

B Serving cached static HTML pages

C Using inline CSS without caching

D Loading all scripts synchronously

DevTools: Network and Performance panels

How to check: Open DevTools, reload page with Network tab open, check if assets are served from cache (status 200 from disk cache). Use Performance tab to measure server response and load times.

What to look for: Look for reduced server response times, assets loaded from cache, and faster Largest Contentful Paint (LCP) times.

Practice

1. What is the main purpose of caching in WordPress?

easy

A. To speed up the website by saving copies of pages or data

B. To increase the size of the website database

C. To delete old posts automatically

D. To change the website theme dynamically

Solution

1. Step 1: Understand caching concept

   Caching stores copies of pages or data to avoid repeated processing.

2. Step 2: Identify caching benefit

   By saving copies, the website loads faster for visitors.

3. Final Answer:

   To speed up the website by saving copies of pages or data -> Option A

4. Quick Check:

   Caching = Speed up site [OK]

Hint: Caching saves copies to load pages faster [OK]

Common Mistakes:

• Thinking caching deletes content
• Believing caching increases database size
• Confusing caching with theme changes

2. Which of the following is the correct way to clear the WordPress cache using a plugin?

easy

A. Change the site URL in settings

B. Click the 'Clear Cache' button in the caching plugin settings

C. Delete all posts from the dashboard

D. Deactivate all plugins except caching

Solution

1. Step 1: Identify cache clearing method

   Caching plugins provide a 'Clear Cache' button to remove saved copies.

2. Step 2: Recognize incorrect options

   Deleting posts, changing URL, or deactivating plugins do not clear cache properly.

3. Final Answer:

   Click the 'Clear Cache' button in the caching plugin settings -> Option B

4. Quick Check:

   Clear cache = Use plugin button [OK]

Hint: Use plugin's clear cache button to refresh content [OK]

Common Mistakes:

• Deleting posts thinking it clears cache
• Changing site URL to fix cache
• Deactivating unrelated plugins

3. Consider this code snippet in a WordPress theme's functions.php file:

function get_cached_data() {
  $cache_key = 'my_data';
  $data = wp_cache_get($cache_key);
  if ($data === false) {
    $data = 'Expensive data';
    wp_cache_set($cache_key, $data, '', 3600);
  }
  return $data;
}

echo get_cached_data();

What will this code output on the first call?

medium

A. An error message

B. false

C. null

D. Expensive data

Solution

1. Step 1: Check cache retrieval

   On first call, wp_cache_get returns false because cache is empty.

2. Step 2: Set and return data

   Since cache is empty, 'Expensive data' is set and returned.

3. Final Answer:

   Expensive data -> Option D

4. Quick Check:

   First call returns new data [OK]

Hint: First cache get returns false, so data is set and returned [OK]

Common Mistakes:

• Assuming cache returns null instead of false
• Expecting error on missing cache
• Thinking cache returns old data on first call

4. You added caching to your WordPress site, but after updating content, visitors still see old pages. What is the likely problem?

medium

A. The site URL is incorrect

B. The theme is incompatible with WordPress

C. Cache was not cleared after content update

D. The database is corrupted

Solution

1. Step 1: Understand caching effect

   Caching saves old page copies to speed up loading.

2. Step 2: Identify update issue

   If cache is not cleared after content changes, old pages show to visitors.

3. Final Answer:

   Cache was not cleared after content update -> Option C

4. Quick Check:

   Old pages = Cache not cleared [OK]

Hint: Always clear cache after content updates [OK]

Common Mistakes:

• Blaming theme for caching issues
• Assuming database corruption causes old pages
• Thinking site URL affects caching

5. You want to improve your WordPress site's speed by caching database query results for 10 minutes. Which approach is best?

hard

A. Use wp_cache_set() with a 600-second expiration after fetching query results

B. Disable all caching plugins and rely on browser cache only

C. Manually save query results in a text file and read it each time

D. Increase PHP memory limit to store all queries in RAM

Solution

1. Step 1: Identify caching method for query results

   wp_cache_set() stores data in WordPress object cache with expiration time.

2. Step 2: Set expiration for 10 minutes

   600 seconds equals 10 minutes, so setting expiration to 600 caches results properly.

3. Step 3: Evaluate other options

   Disabling plugins loses caching benefits; manual file saves are inefficient; increasing memory doesn't cache queries automatically.

4. Final Answer:

   Use wp_cache_set() with a 600-second expiration after fetching query results -> Option A

5. Quick Check:

   Cache query with wp_cache_set + 600s [OK]

Hint: Use wp_cache_set with expiration for timed caching [OK]

Common Mistakes:

• Disabling caching plugins thinking it helps
• Trying manual file caching instead of built-in cache
• Increasing memory without caching logic