Collaboration: Replace post meta storage with dedicated database table

src/wp-admin/admin.php

@@ -113,6 +113,14 @@
 	wp_schedule_event( time(), 'daily', 'delete_expired_transients' );
 }
 
+// Schedule collaboration data cleanup.
+if ( wp_is_collaboration_enabled()
+	&& ! wp_next_scheduled( 'wp_delete_old_collaboration_data' )
+	&& ! wp_installing()
+) {
+	wp_schedule_event( time(), 'daily', 'wp_delete_old_collaboration_data' );
+}
+
 set_screen_options();
 
 $date_format = __( 'F j, Y' );

src/wp-admin/includes/schema.php

@@ -186,6 +186,19 @@ function wp_get_db_schema( $scope = 'all', $blog_id = null ) {
 	KEY post_parent (post_parent),
 	KEY post_author (post_author),
 	KEY type_status_author (post_type,post_status,post_author)
+) $charset_collate;
+CREATE TABLE $wpdb->collaboration (
+	id bigint(20) unsigned NOT NULL auto_increment,
+	room varchar($max_index_length) NOT NULL default '',
+	type varchar(32) NOT NULL default '',
+	client_id varchar(32) NOT NULL default '',
+	user_id bigint(20) unsigned NOT NULL default '0',
+	data longtext NOT NULL,
+	date_gmt datetime NOT NULL default '0000-00-00 00:00:00',
+	PRIMARY KEY  (id),
+	KEY type_client_id (type,client_id),
+	KEY room (room,id),
+	KEY date_gmt (date_gmt)
 ) $charset_collate;\n";
 
 	// Single site users table. The multisite flavor of the users table is handled below.

src/wp-admin/includes/upgrade.php

@@ -886,7 +886,7 @@ function upgrade_all() {
 		upgrade_682();
 	}
 
-	if ( $wp_current_db_version < 61644 ) {
+	if ( $wp_current_db_version < 61841 ) {
 		upgrade_700();
 	}
 

src/wp-includes/class-wpdb.php

@@ -299,6 +299,7 @@ class wpdb {
 		'term_relationships',
 		'termmeta',
 		'commentmeta',
+		'collaboration',
 	);
 
 	/**
@@ -404,6 +405,15 @@ class wpdb {
 	 */
 	public $posts;
 
+	/**
+	 * WordPress Collaboration table.
+	 *
+	 * @since 7.0.0
+	 *
+	 * @var string
+	 */
+	public $collaboration;
+
 	/**
 	 * WordPress Terms table.
 	 *

src/wp-includes/collaboration.php

@@ -11,7 +11,8 @@
  *
  * If the WP_ALLOW_COLLABORATION constant is false,
  * collaboration is always disabled regardless of the database option.
- * Otherwise, falls back to the 'wp_collaboration_enabled' option.
+ * Otherwise, the feature requires both the 'wp_collaboration_enabled'
+ * option and the database schema introduced in db_version 61841.
  *
  * @since 7.0.0
  *
@@ -20,7 +21,8 @@
 function wp_is_collaboration_enabled() {
 	return (
 		wp_is_collaboration_allowed() &&
-		(bool) get_option( 'wp_collaboration_enabled' )
+		get_option( 'wp_collaboration_enabled' ) &&
+		get_option( 'db_version' ) >= 61841
 	);
 }
 
@@ -34,7 +36,7 @@ function wp_is_collaboration_enabled() {
  *
  * @since 7.0.0
  *
- * @return bool Whether real-time collaboration is enabled.
+ * @return bool Whether real-time collaboration is allowed.
  */
 function wp_is_collaboration_allowed() {
 	if ( ! defined( 'WP_ALLOW_COLLABORATION' ) ) {
@@ -83,3 +85,41 @@ function wp_collaboration_inject_setting() {
 		'after'
 	);
 }
+
+/**
+ * Deletes stale collaboration data from the collaboration table.
+ *
+ * Removes non-awareness rows older than 7 days and awareness rows older
+ * than 60 seconds. Rows left behind by abandoned collaborative editing
+ * sessions are cleaned up to prevent unbounded table growth.
+ *
+ * @since 7.0.0
+ */
+function wp_delete_old_collaboration_data() {
+	global $wpdb;
+
+	if ( ! wp_is_collaboration_enabled() ) {
+		/*
+		 * Collaboration was enabled in the past but has since been disabled.
+		 * Unschedule the cron job prior to clean up so this callback does not
+		 * continue to run.
+		 */
+		wp_clear_scheduled_hook( 'wp_delete_old_collaboration_data' );
+	}
+
+	/* Clean up rows older than 7 days. */
+	$wpdb->query(
+		$wpdb->prepare(
+			"DELETE FROM {$wpdb->collaboration} WHERE date_gmt < %s",
+			gmdate( 'Y-m-d H:i:s', time() - WEEK_IN_SECONDS )
+		)
+	);
+
+	// Clean up awareness rows older than 60 seconds.
+	$wpdb->query(
+		$wpdb->prepare(
+			"DELETE FROM {$wpdb->collaboration} WHERE type = 'awareness' AND date_gmt < %s",
+			gmdate( 'Y-m-d H:i:s', time() - 60 )
+		)
+	);
+}