Fragment Caching in WordPress

Fragment caching is useful for caching HTML snippets that are expensive to generate and exist in multiple places on your site. It’s like full page HTML caching, but more granular, and it speeds up dynamic views.

I’ve been using this fragment caching class for a few years now. I optimized it around ease of implementation. I wanted, as much as possible, to be able to identify a slow HTML-outputting block of code, and just wrap this code around it without having to refactor anything about the code inside.

	<?php
	/*
	Usage:
	$frag = new CWS_Fragment_Cache( 'unique-key', 3600 ); // Second param is TTL
	if ( !$frag->output() ) { // NOTE, testing for a return of false
	functions_that_do_stuff_live();
	these_should_echo();
	// IMPORTANT
	$frag->store();
	// YOU CANNOT FORGET THIS. If you do, the site will break.
	}
	*/
	class CWS_Fragment_Cache {
	const GROUP = 'cws-fragments';
	var $key;
	var $ttl;
	public function __construct( $key, $ttl ) {
	$this->key = $key;
	$this->ttl = $ttl;
	}
	public function output() {
	$output = wp_cache_get( $this->key, self::GROUP );
	if ( !empty( $output ) ) {
	// It was in the cache
	echo $output;
	return true;
	} else {
	ob_start();
	return false;
	}
	}
	public function store() {
	$output = ob_get_flush(); // Flushes the buffers
	wp_cache_add( $this->key, $output, self::GROUP, $this->ttl );
	}
	}

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Implementation is pretty easy, and you can reference the comment at the start of the code for that. The only thing to consider is that any variables that alter the output need to be build into the key. It should also be noted that this code assumes you have a persistent object cache backend.