Object Cache for Faster Dynamic Data

Q: What is Dynamic Data?

• Anything that has too be “queried” or looked up
• Content that might look different at different times or to different users
• Content that gets on the page in some way that is complicated or complex

Practical Example: A Recipe Blog

Q: What/why is an Object Cache?

• The problem: Complex database queries are slow, “expensive”, and may have to be made multiple times on a single page load
• The goal: Make the process of fetching that data faster as WordPress “builds” the page
• The method: Saving that data in memory the first time, so it’s ready the next time
• The solution: WP Object Cache

Q: What is NOT in an Object Cache?

• Caching assets like CSS and JS
• Storing images on a CDN
• A page cache that saves the generated HTML

Introducing WP Object Cache

An example in the wild

<?php
function get_cuisines(){
  $cuisines = wp_cache_get( 'our_cuisines' );

  if ( ! $cuisines ) {
    $cuisines = some_expensive_query();
    wp_cache_set( 'our_cuisines', $cuisines );
  }
  return $cuisines;
}Code language: PHP (php)

Q: Doesn’t WordPress do this for me already?

A: Yes! Sometimes! Sort of Unless:

• You’re using custom tables, get_posts, or custom $wpdb calls
• Searches, “random” queries, multi-dimensional queries and queries that aren’t the “main” query
• You’re fetching data from “somewhere else” like an API endpoint (more on this later)

Q: How long does an object cache last?

A: A single page load, unless you use…

• A Persistent Object Cache Plugin
• The Transients API

Persistant Object Cache

Dynamic Data stays in memory over multiple page loads.

• Query Monitor will tell you if you have one
• Your host will probably only work with a specific one
• You’ll need to be much smarter about “clearing your cache” manually and in any custom code

WP Transients API

These look very similar to the WP Object Cache examples.

• Useful for things like storing external API responses
• Can have a ‘maximum’ expiration data
• Will sit in the database if there’s no persistant object cache