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
This commit is contained in:
Boone Gorges
164
wp-includes/class-wp-metadata-lazyloader.php
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164
wp-includes/class-wp-metadata-lazyloader.php
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<?php
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/**
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* Lazyloader for object metadata.
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*
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* When loading many objects of a given type, such as posts in a WP_Query loop, it often makes
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* sense to prime various metadata caches at the beginning of the loop. This means fetching all
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* relevant metadata with a single database query, a technique that has the potential to improve
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* performance dramatically in some cases.
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*
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* In cases where the given metadata may not even be used in the loop, we can improve performance
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* even more by only priming the metadata cache for affected items the first time a piece of metadata
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* is requested - ie, by lazyloading it. So, for example, comment meta may not be loaded into the
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* cache in the comments section of a post until the first time get_comment_meta() is called in the
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* context of the comment loop.
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*
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* WP uses the WP_Metadata_Lazyloader class to queue objects for metadata cache priming. The class
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* then detects the relevant get_*_meta() function call, and queries the metadata of all queued objects.
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*
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* Do not access this class directly. Use the wp_metadata_lazyloader() function.
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*
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* @since 4.5.0
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*/
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class WP_Metadata_Lazyloader {
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/**
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* Pending objects queue.
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*
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* @since 4.5.0
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* @var array
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*/
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protected $pending_objects;
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/**
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* Settings for supported object types.
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*
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* @since 4.5.0
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* @var array
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*/
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protected $settings = array();
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/**
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* Constructor.
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*
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* @since 4.5.0
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*/
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public function __construct() {
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$this->settings = array(
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'term' => array(
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'filter' => 'get_term_metadata',
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'callback' => array( $this, 'lazyload_term_meta' ),
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),
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'comment' => array(
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'filter' => 'get_comment_metadata',
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'callback' => array( $this, 'lazyload_comment_meta' ),
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),
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);
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}
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/**
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* Add objects to the metadata lazyload queue.
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*
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* @since 4.5.0
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*
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* @param string $object_type Type of object whose meta is to be lazyloaded. Accepts 'term' or 'comment'.
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* @param array $object_ids Array of object IDs.
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* @return bool|WP_Error True on success, WP_Error on failure.
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*/
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public function queue_objects( $object_type, $object_ids ) {
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if ( ! isset( $this->settings[ $object_type ] ) ) {
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return new WP_Error( 'invalid_object_type', __( 'Invalid object type' ) );
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}
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$type_settings = $this->settings[ $object_type ];
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if ( ! isset( $this->pending_objects[ $object_type ] ) ) {
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$this->pending_objects[ $object_type ] = array();
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}
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foreach ( $object_ids as $object_id ) {
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// Keyed by ID for faster lookup.
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if ( ! isset( $this->pending_objects[ $object_type ][ $object_id ] ) ) {
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$this->pending_objects[ $object_type ][ $object_id ] = 1;
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}
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}
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add_filter( $type_settings['filter'], $type_settings['callback'] );
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/**
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* Fires after objects are added to the metadata lazyload queue.
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*
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* @since 4.5.0
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*
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* @param array $object_ids Object IDs.
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* @param string $object_type Type of object being queued.
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* @param WP_Metadata_Lazyloader $lazyloader The lazyloader object.
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*/
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do_action( 'metadata_lazyloader_queued_objects', $object_ids, $object_type, $this );
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}
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/**
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* Reset lazyload queue for a given object type.
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*
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* @since 4.5.0
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*
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* @param string $object_type Object type. Accepts 'comment' or 'term'.
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* @return bool|WP_Error True on success, WP_Error on failure.
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*/
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public function reset_queue( $object_type ) {
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if ( ! isset( $this->settings[ $object_type ] ) ) {
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return new WP_Error( 'invalid_object_type', __( 'Invalid object type' ) );
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}
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$type_settings = $this->settings[ $object_type ];
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$this->pending_objects[ $object_type ] = array();
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remove_filter( $type_settings['filter'], $type_settings['callback'] );
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}
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/**
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* Lazyloads term meta for queued terms.
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*
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* This method is public so that it can be used as a filter callback. As a rule, there
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* is no need to invoke it directly.
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*
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* @since 4.5.0
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* @access public
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*
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* @param mixed $check The `$check` param passed from the 'get_term_metadata' hook.
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* @return mixed In order not to short-circuit `get_metadata()`. Generally, this is `null`, but it could be
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* another value if filtered by a plugin.
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*/
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public function lazyload_term_meta( $check ) {
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if ( ! empty( $this->pending_objects['term'] ) ) {
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update_termmeta_cache( array_keys( $this->pending_objects['term'] ) );
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// No need to run again for this set of terms.
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$this->reset_queue( 'term' );
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}
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return $check;
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}
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/**
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* Lazyload comment meta for queued comments.
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*
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* This method is public so that it can be used as a filter callback. As a rule, there is no need to invoke it
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* directly, from either inside or outside the `WP_Query` object.
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*
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* @since 4.5.0
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*
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* @param mixed $check The `$check` param passed from the 'get_comment_metadata' hook.
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* @return mixed The original value of `$check`, so as not to short-circuit `get_comment_metadata()`.
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*/
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public function lazyload_comment_meta( $check ) {
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if ( ! empty( $this->pending_objects['comment'] ) ) {
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update_meta_cache( 'comment', array_keys( $this->pending_objects['comment'] ) );
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// No need to run again for this set of comments.
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$this->reset_queue( 'comment' );
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}
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return $check;
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}
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}
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