Performance/Caching

Timber, especially in conjunction with WordPress and Twig, offers a variety of caching strategies to optimize performance. Here’s a quick rundown of some of the options, ranked in order of most-broad to most-focused.

tl;dr

In my tests with Debug Bar, Timber has no measurable performance hit. Everything compiles to PHP. @fabpot has an overview of the performance costs on his blog (scroll down to the table).

Cache Everything

You can still use plugins like W3 Total Cache in conjunction with Timber. In most settings, this will skip the Twig/Timber layer of your files and serve static pages via whatever mechanism the plugin or settings dictate.

Cache the Entire Twig File and Data

When rendering, use the $expires argument in Timber::render. For example:

<?php
$context['posts'] = Timber::get_posts();
Timber::render( 'index.twig', $context, 600 );

In this example, Timber will cache the template for 10 minutes (600 / 60 = 10). But here’s the cool part: Timber hashes the fields in the view context. This means that as soon as the data changes, the cache is automatically invalidated. Yay!

This method is very effective, but crude - the whole template is cached. So if you have any context dependent sub-views (eg. current user), this mode won’t do.

Set cache mode

As a fourth parameter for Timber::render(), you can set the $cache_mode.

<?php
Timber::render( $filenames, $data, $expires, $cache_mode );

The following cache modes are available:

Mode Description
Timber\Loader::CACHE_NONE Disable caching
Timber\Loader::CACHE_OBJECT WP Object Cache
Timber\Loader::CACHE_TRANSIENT Transients
Timber\Loader::CACHE_SITE_TRANSIENT Network wide transients
Timber\Loader::CACHE_USE_DEFAULT Use whatever caching mechanism is set as the default for Timber\Loader, the default is CACHE_TRANSIENT.

Cache Parts of the Twig File and Data

This method implements the Twig Cache Extension. It adds the cache tag, for use in templates. Best shown by example:

{% cache 'index/content' posts %}
    {% for post in posts %}
        {% include ['tease-'~post.post_type~'.twig', 'tease.twig'] %}
    {% endfor %}
{% endcache %}

'index/content' will be used as annotation (label) for the cache, while posts will be encoded with all its public fields. You can use anything for the label (“foo”, “elephant”, “single-posts”, whatever).

The mechanism behind it is the same as with render - the cache key is determined based on a hash of the object/array passed in (in the above example posts).

The cache method used is always the default mode, set using the bespoke filter (by default, transient cache).

This method allows for very fine-grained control over what parts of templates are being cached and which are not. When applied on resource-intensive sections, the performance difference is huge.

In your cache, the eventual key will be:

<?php
$annotation . '__GCS__' . $key

That is in this scenario:

<?php
'index/content__GCS__' . md5( json_encode( $context['post'] ) )

Extra: TimberKeyGeneratorInterface

Instead of hashing a whole object, you can specify the cache key in the object itself. If the object implements TimberKeyGeneratorInterface, it can pass a unique key through the method get_cache_key. That way a class can for example simply pass 'last_updated' as the unique key. If arrays contain the key _cache_key, that one is used as cache key.

This may save yet another few processor cycles.

Cache the Twig File (but not the data)

Every time you render a .twig file, Twig compiles all the HTML tags and variables into a big, nasty blob of function calls and echo statements that actually gets run by PHP. In general, this is pretty efficient. However, you can cache the resulting PHP blob by turning on Twig’s cache via:

functions.php

<?php
if ( class_exists( 'Timber' ) ){
	Timber::$cache = true;
}

You can look in your your /wp-content/plugins/timber/twig-cache directory to see what these files look like.

This does not cache the contents of the variables. This is recommended as a last-step in the production process. Once enabled, any change you make to a .twig file (just tweaking the HTML for example) will not go live until the cache is flushed.

Cache the PHP data

Sometimes the most expensive parts of the operations are generating the data needed to populate the twig template. You can of course use WordPress’s default Transient API to store this data.

You can also use some syntactic sugar to make the checking/saving/retrieving of transient data a bit easier:

home.php

<?php

$context = Timber::get_context();

$context['main_stories'] = TimberHelper::transient( 'main_stories', function(){
    $posts = Timber::get_posts();

    // As an example, do something expensive with these posts
    $extra_teases = get_field( 'my_extra_teases', 'options' );

    foreach( $extra_teases as &$tease ){
        $tease = new Timber\Post( $tease );
    }

    $main_stories = array();
    $main_stories['posts'] = $posts;
    $main_stories['extra_teases'] = $extra_teases;

    return $main_stories;
}, 600 );

Timber::render( 'home.twig', $context );

Here main_stories is a totally made-up variable. It could be called foo, bar, elephant, etc.

Measuring Performance

Some tools like Debug Bar may not properly measure performance because its data (as in, the actual HTML it’s generating to tell you the timing, number of queries, etc.) is swept-up by the page’s cache.

Timber provides some quick shortcuts to measure page timing. Here’s an example of them in action:

single.php

<?php
// This generates a starting time
$start = TimberHelper::start_timer();

$context = Timber::get_context();
$context['post'] = Timber::get_post();
$context['whatever'] = get_my_foo();

Timber::render( 'single.twig', $context, 600 );

// This reports the time diff by passing the $start time
echo TimberHelper::stop_timer( $start);