What is WordPress at Scale?

The Problem

Page Caching is Lovely

Page Caching is Limiting

github.com/dashboard/issues

Page caching is effective

but cannot work in these scenarios

What Now?

Solution 1: Hardware

Expensive

Hard to scale

Solution 2: "Fragment Caching"

Partial page caching

using object caching

<div id="latest-activity">
<?php
$activity = wp_cache_get( 'latest_activity' );
if ( false === $activity ) {
    $activity = get_latest_activity();
    wp_cache_set( 'latest_activity', $activity, '', 3600 );
}
echo $activity;
?>
</div>

Cache user based variants

<div id="latest-activity">
<?php
$user_id  = get_current_user_id();
$activity = wp_cache_get( 'latest_activity', $user_id );
if ( false === $activity ) {
    $activity = get_latest_activity();
    wp_cache_set( 'latest_activity', $activity, $user_id, 3600 );
}
echo $activity;
?>
</div>

TLC transients

Fragment caching class by Jaquith

Pods framework

Works well

Easy to understand

Always load all of WordPress

Not very performant

Solution 3: Clever Advanced Cache

Daniel Dvorkin

advanced-cached.php implements a page cache for WordPress

Loaded after 1% of WordPress is loaded

<div id="latest-activity">
    <nocache callback="get_latest_activity"></nocache>
</div>

If metadata does not exist, strip the tags and display

If metadata exists, generate the block

<div id="latest-activity">
    <nocache is_user_logged_in callback="get_latest_activity">
        <p>Activity feed is not available.</p>
    </nocache>
</div>

Uses core standards

"callback" method is may present problems

Solution 4: Edge Side Includes

Partial Page Templating

Embed ESI tags in the template

<div id="latest-activity">
    <?php 
    // Loads partial-activity.php
    get_template_part( 'partial', 'activity' ); 
    ?>
</div>

<?php if ( isset( $_GET['partial'] ) && 'activity' === $_GET['partial'] ) : ?>
    <?php echo get_latest_activity(); ?>
<?php else : ?>
    <esi:remove>
        <p>Activity feed is not available.</p>
    </esi:remove>
    <!--esi
    <esi:include src="<?php echo site_url( '/?partial=activity' ); ?>" />
    -->
<?php endif; ?>

<div id="latest-activity">
    <esi:remove>
        <p>Activity feed is not available.</p>
    </esi:remove>
    <!--esi
    <esi:include src="<?php echo site_url( '/?partial=activity' ); ?>" />
    -->
</div>

function zdt_page_template_redirect() {
    if ( isset( $_GET['partial'] ) ) {
        $sanitize_partial = sanitize_key( $_GET['partial'] );
        get_template_part( 'partial', $sanitize_partial );
        exit();
    }
}

add_action( 'template_redirect', 'zdt_page_template_redirect' );

<?php if ( isset( $_GET['partial'] ) && 'activity' === $_GET['partial'] ) : ?>
    <?php echo get_latest_activity(); ?>
<?php else : ?>
    <esi:remove>
        <p>Activity feed is not available.</p>
    </esi:remove>
    <!--esi
    <esi:include src="<?php echo site_url( '/?partial=activity' ); ?>" />
    -->
<?php endif; ?>

Adheres to WordPress standards

Many partials can lead to many WordPress loads

You Decide

There is no right answer

There are a lot of wrong answers

Each app needs its own technique

Zack Tollman

The Theme Foundry

@tollmanz

tollmanz.github.io/wcyvr-2013

tollmanz.com/partial-page-templating-in-wordpress