Caching strategies in Wordpress - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is caching in WordPress?

Caching in WordPress means saving copies of your website pages or data so they load faster next time someone visits. It helps reduce the work your server does and speeds up your site.

beginner

Name two common types of caching used in WordPress.

Two common types are:
1. Page Caching - saves full HTML pages.
2. Object Caching - saves database query results or objects.

intermediate

What is the difference between server-side caching and browser caching?

Server-side caching stores data on the web server to speed up responses.
Browser caching stores files on the visitor's device to avoid re-downloading them on repeat visits.

beginner

How does a caching plugin improve WordPress performance?

A caching plugin creates and serves saved copies of pages or data quickly, reducing the need to run heavy database queries or PHP code every time. This makes pages load faster for visitors.

intermediate

What is cache invalidation and why is it important?

Cache invalidation means clearing or updating cached data when the original content changes. It is important so visitors see the latest content and not outdated pages.

Which caching type saves full HTML pages in WordPress?

A Page Caching

B Object Caching

C Browser Caching

D Opcode Caching

Page caching saves the entire HTML page to serve it quickly without rebuilding it each time.

What does object caching store?

A Full HTML pages

B Browser cookies

C Images and CSS files

D Database query results or objects

Object caching stores database query results or PHP objects to speed up repeated data access.

Why is cache invalidation necessary?

A To speed up the server

B To increase browser storage

C To clear outdated cached content

D To compress images

Cache invalidation clears or updates cached content so visitors see the latest version.

Which of these is NOT a caching strategy in WordPress?

A SQL Injection

B Object Caching

C Browser Caching

D Page Caching

SQL Injection is a security issue, not a caching strategy.

Where is browser caching data stored?

A On the web server

B In the visitor's device

C In the WordPress database

D In the caching plugin settings

Browser caching stores files on the visitor's device to avoid re-downloading them.

Explain how caching improves WordPress website speed and user experience.

Think about what happens when a website doesn't have to rebuild pages every time.

Describe the difference between page caching and object caching in WordPress.

Consider what each type stores and how it helps.

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