RTC: Transients for awareness and JIT meta cache flushing

src/wp-includes/class-wp-query.php

@@ -2473,6 +2473,20 @@ public function get_posts() {
 			$clauses = $this->meta_query->get_sql( 'post', $wpdb->posts, 'ID', $this );
 			$join   .= $clauses['join'];
 			$where  .= $clauses['where'];
+
+			/*
+			 * Determine if meta queries require just-in-time cache invalidation.
+			 *
+			 * If the most recent modification of post meta (addition, update or deletion) was of a meta key
+			 * that uses jit cache invalidation, then the meta query cache will be considered stale and the
+			 * post-query cache group flushed by changing the posts' last changed time.
+			 *
+			 * The cache is considered up to date if the `wp_query_meta_query_updated` cache key in the `post_meta`
+			 * group returns `true`, otherwise the cache will be considered stale.
+			 */
+			if ( ! wp_cache_get( 'wp_query_meta_query_updated', 'post_meta' ) ) {
+				wp_cache_set_posts_last_changed();
+			}
 		}
 
 		$rand = ( isset( $query_vars['orderby'] ) && 'rand' === $query_vars['orderby'] );

src/wp-includes/collaboration/class-wp-http-polling-sync-server.php

@@ -355,12 +355,33 @@ private function process_awareness_update( string $room, int $client_id, ?array
 			$updated_awareness[] = $entry;
 		}
 
+		/**
+		 * Filters granularity used for rounding up a client's awareness timestamp.
+		 *
+		 * Modifies the granularity used when recording the latest time a client updates their
+		 * awareness state. This allows implementations to increase or reduce the granularity
+		 * of awareness updates for the desired balance of real-time updates and server load.
+		 *
+		 * The default database granularity of 10 seconds limits the number of writes to the
+		 * database as WordPress only makes the database call if the transient has changed.
+		 * Increasing the granularity by lowering this number will increase the number of
+		 * database writes.
+		 *
+		 * @since 7.0.0
+		 *
+		 * @param int $granularity Granularity in seconds. Default 10.
+		 */
+		$granularity = absint( apply_filters( 'wp_sync_awareness_timestamp_granularity', 10 ) );
+		if ( 0 === $granularity ) {
+			$granularity = 1;
+		}
+
 		// Add this client's awareness state.
 		if ( null !== $awareness_update ) {
 			$updated_awareness[] = array(
 				'client_id'  => $client_id,
 				'state'      => $awareness_update,
-				'updated_at' => $current_time,
+				'updated_at' => ceil( $current_time / $granularity ) * $granularity, // Round up to nearest granularity to reduce database churn.
 				'wp_user_id' => get_current_user_id(),
 			);
 		}

src/wp-includes/collaboration/class-wp-sync-post-meta-storage.php

@@ -30,7 +30,7 @@ class WP_Sync_Post_Meta_Storage implements WP_Sync_Storage {
 	 * @since 7.0.0
 	 * @var string
 	 */
-	const AWARENESS_META_KEY = 'wp_sync_awareness_state';
+	const AWARENESS_TRANSIENT_PREFIX = 'wp_sync_awareness';
 
 	/**
 	 * Meta key for sync updates.
@@ -69,73 +69,39 @@ class WP_Sync_Post_Meta_Storage implements WP_Sync_Storage {
 	 *
 	 * @since 7.0.0
 	 *
-	 * @global wpdb $wpdb WordPress database abstraction object.
-	 *
 	 * @param string $room   Room identifier.
 	 * @param mixed  $update Sync update.
 	 * @return bool True on success, false on failure.
 	 */
 	public function add_update( string $room, $update ): bool {
-		global $wpdb;
-
 		$post_id = $this->get_storage_post_id( $room );
 		if ( null === $post_id ) {
 			return false;
 		}
 
-		// Use direct database operation to avoid cache invalidation performed by
-		// post meta functions (`wp_cache_set_posts_last_changed()` and direct
-		// `wp_cache_delete()` calls).
-		return (bool) $wpdb->insert(
-			$wpdb->postmeta,
-			array(
-				'post_id'    => $post_id,
-				'meta_key'   => self::SYNC_UPDATE_META_KEY,
-				'meta_value' => wp_json_encode( $update ),
-			),
-			array( '%d', '%s', '%s' )
-		);
+		$meta_id = add_post_meta( $post_id, wp_slash( self::SYNC_UPDATE_META_KEY ), wp_slash( $update ), false );
+
+		return (bool) $meta_id;
 	}
 
 	/**
 	 * Gets awareness state for a given room.
 	 *
 	 * @since 7.0.0
 	 *
-	 * @global wpdb $wpdb WordPress database abstraction object.
-	 *
 	 * @param string $room Room identifier.
 	 * @return array<int, mixed> Awareness state.
 	 */
 	public function get_awareness_state( string $room ): array {
-		global $wpdb;
-
-		$post_id = $this->get_storage_post_id( $room );
-		if ( null === $post_id ) {
-			return array();
-		}
-
-		// Use direct database operation to avoid updating the post meta cache.
-		// ORDER BY meta_id DESC ensures the latest row wins if duplicates exist
-		// from a past race condition in set_awareness_state().
-		$meta_value = $wpdb->get_var(
-			$wpdb->prepare(
-				"SELECT meta_value FROM $wpdb->postmeta WHERE post_id = %d AND meta_key = %s ORDER BY meta_id DESC LIMIT 1",
-				$post_id,
-				self::AWARENESS_META_KEY
-			)
-		);
-
-		if ( null === $meta_value ) {
-			return array();
-		}
-
-		$awareness = json_decode( $meta_value, true );
+		$room_hash = md5( $room ); // Not used for cryptographic purposes.
+		$awareness = get_transient( self::AWARENESS_TRANSIENT_PREFIX . ":{$room_hash}" );
 
 		if ( ! is_array( $awareness ) ) {
 			return array();
 		}
 
+		// Deterministic ordering of transient data.
+		$awareness = wp_list_sort( $awareness, 'client_id' );
 		return array_values( $awareness );
 	}
 
@@ -144,54 +110,24 @@ public function get_awareness_state( string $room ): array {
 	 *
 	 * @since 7.0.0
 	 *
-	 * @global wpdb $wpdb WordPress database abstraction object.
-	 *
 	 * @param string            $room      Room identifier.
 	 * @param array<int, mixed> $awareness Serializable awareness state.
 	 * @return bool True on success, false on failure.
 	 */
 	public function set_awareness_state( string $room, array $awareness ): bool {
-		global $wpdb;
-
-		$post_id = $this->get_storage_post_id( $room );
-		if ( null === $post_id ) {
-			return false;
-		}
-
-		// Use direct database operation to avoid cache invalidation performed by
-		// post meta functions (`wp_cache_set_posts_last_changed()` and direct
-		// `wp_cache_delete()` calls).
-		//
-		// If two concurrent requests both see no row and both INSERT, the
-		// duplicate is harmless: get_awareness_state() reads the latest row
-		// (ORDER BY meta_id DESC).
-		$meta_id = $wpdb->get_var(
-			$wpdb->prepare(
-				"SELECT meta_id FROM $wpdb->postmeta WHERE post_id = %d AND meta_key = %s ORDER BY meta_id DESC LIMIT 1",
-				$post_id,
-				self::AWARENESS_META_KEY
-			)
-		);
-
-		if ( $meta_id ) {
-			return (bool) $wpdb->update(
-				$wpdb->postmeta,
-				array( 'meta_value' => wp_json_encode( $awareness ) ),
-				array( 'meta_id' => $meta_id ),
-				array( '%s' ),
-				array( '%d' )
-			);
-		}
-
-		return (bool) $wpdb->insert(
-			$wpdb->postmeta,
-			array(
-				'post_id'    => $post_id,
-				'meta_key'   => self::AWARENESS_META_KEY,
-				'meta_value' => wp_json_encode( $awareness ),
-			),
-			array( '%d', '%s', '%s' )
-		);
+		$room_hash = md5( $room ); // Not used for cryptographic purposes.
+		// Deterministic ordering of transient data.
+		$awareness = wp_list_sort( $awareness, 'client_id' );
+
+		/*
+		 * Maintain transient for longer than awareness.
+		 *
+		 * Recently used rooms are more likely to be used again soon. Maintaining the
+		 * transient longer than the awareness can avoid adding new entries in the options
+		 * table unnecessarily.
+		 */
+		set_transient( self::AWARENESS_TRANSIENT_PREFIX . ":{$room_hash}", $awareness, DAY_IN_SECONDS );
+		return true;
 	}
 
 	/**
@@ -281,8 +217,6 @@ public function get_update_count( string $room ): int {
 	 *
 	 * @since 7.0.0
 	 *
-	 * @global wpdb $wpdb WordPress database abstraction object.
-	 *
 	 * @param string $room   Room identifier.
 	 * @param int    $cursor Return updates after this cursor (meta_id).
 	 * @return array<int, mixed> Sync updates.
@@ -332,10 +266,7 @@ public function get_updates_after_cursor( string $room, int $cursor ): array {
 
 		$updates = array();
 		foreach ( $rows as $row ) {
-			$decoded = json_decode( $row->meta_value, true );
-			if ( null !== $decoded ) {
-				$updates[] = $decoded;
-			}
+			$updates[] = maybe_unserialize( $row->meta_value );
 		}
 
 		return $updates;
@@ -346,8 +277,6 @@ public function get_updates_after_cursor( string $room, int $cursor ): array {
 	 *
 	 * @since 7.0.0
 	 *
-	 * @global wpdb $wpdb WordPress database abstraction object.
-	 *
 	 * @param string $room   Room identifier.
 	 * @param int    $cursor Remove updates with meta_id < this cursor.
 	 * @return bool True on success, false on failure.
@@ -373,6 +302,7 @@ public function remove_updates_before_cursor( string $room, int $cursor ): bool
 			return false;
 		}
 
+		wp_cache_maybe_set_posts_last_changed_following_post_meta_update( array(), $post_id, self::SYNC_UPDATE_META_KEY );
 		return true;
 	}
 }

src/wp-includes/default-filters.php

@@ -122,9 +122,10 @@
 }
 
 // Post meta.
-add_action( 'added_post_meta', 'wp_cache_set_posts_last_changed' );
-add_action( 'updated_post_meta', 'wp_cache_set_posts_last_changed' );
-add_action( 'deleted_post_meta', 'wp_cache_set_posts_last_changed' );
+add_action( 'added_post_meta', 'wp_cache_maybe_set_posts_last_changed_following_post_meta_update', 10, 3 );
+add_action( 'updated_post_meta', 'wp_cache_maybe_set_posts_last_changed_following_post_meta_update', 10, 3 );
+add_action( 'deleted_post_meta', 'wp_cache_maybe_set_posts_last_changed_following_post_meta_update', 10, 3 );
+add_action( 'init', 'wp_create_initial_post_meta' );
 
 // User meta.
 add_action( 'added_user_meta', 'wp_cache_set_users_last_changed' );
@@ -769,9 +770,6 @@
 // User preferences.
 add_action( 'init', 'wp_register_persisted_preferences_meta' );
 
-// CPT wp_block custom postmeta field.
-add_action( 'init', 'wp_create_initial_post_meta' );
-
 // Include revisioned meta when considering whether a post revision has changed.
 add_filter( 'wp_save_post_revision_post_has_changed', 'wp_check_revisioned_meta_fields_have_changed', 10, 3 );
 

src/wp-includes/meta.php

@@ -1396,6 +1396,7 @@ function sanitize_meta( $meta_key, $meta_value, $object_type, $object_subtype =
  * @since 5.5.0 The `$default` argument was added to the arguments array.
  * @since 6.4.0 The `$revisions_enabled` argument was added to the arguments array.
  * @since 6.7.0 The `label` argument was added to the arguments array.
+ * @since 7.0.0 The `$jit_cache_invalidation` argument was added to the arguments array.
  *
  * @global array $wp_meta_keys Global registry for meta keys.
  *
@@ -1405,27 +1406,30 @@ function sanitize_meta( $meta_key, $meta_value, $object_type, $object_subtype =
  * @param array        $args {
  *     Data used to describe the meta key when registered.
  *
- *     @type string     $object_subtype    A subtype; e.g. if the object type is "post", the post type. If left empty,
- *                                         the meta key will be registered on the entire object type. Default empty.
- *     @type string     $type              The type of data associated with this meta key.
- *                                         Valid values are 'string', 'boolean', 'integer', 'number', 'array', and 'object'.
- *     @type string     $label             A human-readable label of the data attached to this meta key.
- *     @type string     $description       A description of the data attached to this meta key.
- *     @type bool       $single            Whether the meta key has one value per object, or an array of values per object.
- *     @type mixed      $default           The default value returned from get_metadata() if no value has been set yet.
- *                                         When using a non-single meta key, the default value is for the first entry.
- *                                         In other words, when calling get_metadata() with `$single` set to `false`,
- *                                         the default value given here will be wrapped in an array.
- *     @type callable   $sanitize_callback A function or method to call when sanitizing `$meta_key` data.
- *     @type callable   $auth_callback     Optional. A function or method to call when performing edit_post_meta,
- *                                         add_post_meta, and delete_post_meta capability checks.
- *     @type bool|array $show_in_rest      Whether data associated with this meta key can be considered public and
- *                                         should be accessible via the REST API. A custom post type must also declare
- *                                         support for custom fields for registered meta to be accessible via REST.
- *                                         When registering complex meta values this argument may optionally be an
- *                                         array with 'schema' or 'prepare_callback' keys instead of a boolean.
- *     @type bool       $revisions_enabled Whether to enable revisions support for this meta_key. Can only be used when the
- *                                         object type is 'post'.
+ *     @type string     $object_subtype         A subtype; e.g. if the object type is "post", the post type. If left empty,
+ *                                              the meta key will be registered on the entire object type. Default empty.
+ *     @type string     $type                   The type of data associated with this meta key.
+ *                                              Valid values are 'string', 'boolean', 'integer', 'number', 'array', and 'object'.
+ *     @type string     $label                  A human-readable label of the data attached to this meta key.
+ *     @type string     $description            A description of the data attached to this meta key.
+ *     @type bool       $single                 Whether the meta key has one value per object, or an array of values per object.
+ *     @type mixed      $default                The default value returned from get_metadata() if no value has been set yet.
+ *                                              When using a non-single meta key, the default value is for the first entry.
+ *                                              In other words, when calling get_metadata() with `$single` set to `false`,
+ *                                              the default value given here will be wrapped in an array.
+ *     @type callable   $sanitize_callback      A function or method to call when sanitizing `$meta_key` data.
+ *     @type callable   $auth_callback          Optional. A function or method to call when performing edit_post_meta,
+ *                                              add_post_meta, and delete_post_meta capability checks.
+ *     @type bool|array $show_in_rest           Whether data associated with this meta key can be considered public and
+ *                                              should be accessible via the REST API. A custom post type must also declare
+ *                                              support for custom fields for registered meta to be accessible via REST.
+ *                                              When registering complex meta values this argument may optionally be an
+ *                                              array with 'schema' or 'prepare_callback' keys instead of a boolean.
+ *     @type bool       $revisions_enabled      Whether to enable revisions support for this meta_key. Can only be used when the
+ *                                              object type is 'post'.
+ *     @type bool       $jit_cache_invalidation Whether to enable just-in-time cache invalidation for this meta key. When enabled, the cache
+ *                                              for WP_Query will be invalidated the next time a meta query is run. Can only be used when the
+ *                                              object type is 'post'.
  * }
  * @param string|array $deprecated Deprecated. Use `$args` instead.
  * @return bool True if the meta key was successfully registered in the global array, false if not.
@@ -1450,6 +1454,7 @@ function register_meta( $object_type, $meta_key, $args, $deprecated = null ) {
 		'auth_callback'     => null,
 		'show_in_rest'      => false,
 		'revisions_enabled' => false,
+		'jit_cache_invalidation' => false,
 	);
 
 	// There used to be individual args for sanitize and auth callbacks.
@@ -1508,6 +1513,12 @@ function register_meta( $object_type, $meta_key, $args, $deprecated = null ) {
 		}
 	}
 
+	if ( $args['jit_cache_invalidation'] && 'post' !== $object_type ) {
+		_doing_it_wrong( __FUNCTION__, __( 'Just-in-time cache invalidation for meta keys is only supported with the "post" object type.' ), '7.0.0' );
+
+		return false;
+	}
+
 	// If `auth_callback` is not provided, fall back to `is_protected_meta()`.
 	if ( empty( $args['auth_callback'] ) ) {
 		if ( is_protected_meta( $meta_key, $object_type ) ) {