WordPress/wp-includes/class-wp-metadata-lazyloader.php

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More performance improvements to metadata lazyloading. Comment and term meta lazyloading for `WP_Query` loops, introduced in 4.4, depended on filter callback methods belonging to `WP_Query` objects. This meant storing `WP_Query` objects in the `$wp_filter` global (via `add_filter()`), requiring that PHP retain the objects in memory, even when the local variables would typically be expunged during normal garbage collection. In cases where a large number of `WP_Query` objects were instantiated on a single pageload, and/or where the contents of the `WP_Query` objects were quite large, serious performance issues could result. We skirt this problem by moving metadata lazyloading out of `WP_Query`. The new `WP_Metadata_Lazyloader` class acts as a lazyload queue. Query instances register items whose metadata should be lazyloaded - such as post terms, or comments - and a `WP_Metadata_Lazyloader` method will intercept comment and term meta requests to perform the cache priming. Since `WP_Metadata_Lazyloader` instances are far smaller than `WP_Query` (containing only object IDs), and clean up after themselves far better than the previous `WP_Query` methods (bp only running their callbacks a single time for a given set of queued objects), the resource use is decreased dramatically. See [36525] for an earlier step in this direction. Props lpawlik, stevegrunwell, boonebgorges. Fixes #35816. Built from https://develop.svn.wordpress.org/trunk@36566 git-svn-id: http://core.svn.wordpress.org/trunk@36533 1a063a9b-81f0-0310-95a4-ce76da25c4cd
2016-02-17 23:58:26 +01:00
<?php
/**
* Lazyloader for object metadata.
*
* When loading many objects of a given type, such as posts in a WP_Query loop, it often makes
* sense to prime various metadata caches at the beginning of the loop. This means fetching all
* relevant metadata with a single database query, a technique that has the potential to improve
* performance dramatically in some cases.
*
* In cases where the given metadata may not even be used in the loop, we can improve performance
* even more by only priming the metadata cache for affected items the first time a piece of metadata
* is requested - ie, by lazyloading it. So, for example, comment meta may not be loaded into the
* cache in the comments section of a post until the first time get_comment_meta() is called in the
* context of the comment loop.
*
* WP uses the WP_Metadata_Lazyloader class to queue objects for metadata cache priming. The class
* then detects the relevant get_*_meta() function call, and queries the metadata of all queued objects.
*
* Do not access this class directly. Use the wp_metadata_lazyloader() function.
*
* @since 4.5.0
*/
class WP_Metadata_Lazyloader {
/**
* Pending objects queue.
*
* @since 4.5.0
* @var array
*/
protected $pending_objects;
/**
* Settings for supported object types.
*
* @since 4.5.0
* @var array
*/
protected $settings = array();
/**
* Constructor.
*
* @since 4.5.0
*/
public function __construct() {
$this->settings = array(
'term' => array(
'filter' => 'get_term_metadata',
'callback' => array( $this, 'lazyload_term_meta' ),
),
'comment' => array(
'filter' => 'get_comment_metadata',
'callback' => array( $this, 'lazyload_comment_meta' ),
),
);
}
/**
* Add objects to the metadata lazyload queue.
*
* @since 4.5.0
*
* @param string $object_type Type of object whose meta is to be lazyloaded. Accepts 'term' or 'comment'.
* @param array $object_ids Array of object IDs.
* @return bool|WP_Error True on success, WP_Error on failure.
*/
public function queue_objects( $object_type, $object_ids ) {
if ( ! isset( $this->settings[ $object_type ] ) ) {
return new WP_Error( 'invalid_object_type', __( 'Invalid object type' ) );
}
$type_settings = $this->settings[ $object_type ];
if ( ! isset( $this->pending_objects[ $object_type ] ) ) {
$this->pending_objects[ $object_type ] = array();
}
foreach ( $object_ids as $object_id ) {
// Keyed by ID for faster lookup.
if ( ! isset( $this->pending_objects[ $object_type ][ $object_id ] ) ) {
$this->pending_objects[ $object_type ][ $object_id ] = 1;
}
}
add_filter( $type_settings['filter'], $type_settings['callback'] );
/**
* Fires after objects are added to the metadata lazyload queue.
*
* @since 4.5.0
*
* @param array $object_ids Object IDs.
* @param string $object_type Type of object being queued.
* @param WP_Metadata_Lazyloader $lazyloader The lazyloader object.
*/
do_action( 'metadata_lazyloader_queued_objects', $object_ids, $object_type, $this );
}
/**
* Reset lazyload queue for a given object type.
*
* @since 4.5.0
*
* @param string $object_type Object type. Accepts 'comment' or 'term'.
* @return bool|WP_Error True on success, WP_Error on failure.
*/
public function reset_queue( $object_type ) {
if ( ! isset( $this->settings[ $object_type ] ) ) {
return new WP_Error( 'invalid_object_type', __( 'Invalid object type' ) );
}
$type_settings = $this->settings[ $object_type ];
$this->pending_objects[ $object_type ] = array();
remove_filter( $type_settings['filter'], $type_settings['callback'] );
}
/**
* Lazyloads term meta for queued terms.
*
* This method is public so that it can be used as a filter callback. As a rule, there
* is no need to invoke it directly.
*
* @since 4.5.0
* @access public
*
* @param mixed $check The `$check` param passed from the 'get_term_metadata' hook.
* @return mixed In order not to short-circuit `get_metadata()`. Generally, this is `null`, but it could be
* another value if filtered by a plugin.
*/
public function lazyload_term_meta( $check ) {
if ( ! empty( $this->pending_objects['term'] ) ) {
update_termmeta_cache( array_keys( $this->pending_objects['term'] ) );
// No need to run again for this set of terms.
$this->reset_queue( 'term' );
}
return $check;
}
/**
* Lazyload comment meta for queued comments.
*
* This method is public so that it can be used as a filter callback. As a rule, there is no need to invoke it
* directly, from either inside or outside the `WP_Query` object.
*
* @since 4.5.0
*
* @param mixed $check The `$check` param passed from the 'get_comment_metadata' hook.
* @return mixed The original value of `$check`, so as not to short-circuit `get_comment_metadata()`.
*/
public function lazyload_comment_meta( $check ) {
if ( ! empty( $this->pending_objects['comment'] ) ) {
update_meta_cache( 'comment', array_keys( $this->pending_objects['comment'] ) );
// No need to run again for this set of comments.
$this->reset_queue( 'comment' );
}
return $check;
}
}