[WIP] Collaboration: Migrate real-time storage from post meta to custom tables

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 +186,41 @@ 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;
+/*
+ * Collaboration and awareness use separate tables because they have
+ * opposite uniqueness requirements on the same columns.
+ *
+ * Collaboration rows are append-only: a single client writes many rows
+ * per room over time, so no UNIQUE constraint is possible on (room, client_id).
+ *
+ * Awareness rows require exactly one per client per room. The UNIQUE KEY
+ * on (room, client_id) enables INSERT ... ON DUPLICATE KEY UPDATE for
+ * atomic upsert, preventing the duplicate-row race condition that occurs
+ * with DELETE+INSERT under concurrent requests.
+ */
+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 '',
+	update_value longtext NOT NULL,
+	created_at datetime NOT NULL default '0000-00-00 00:00:00',
+	PRIMARY KEY  (id),
+	KEY room (room,id),
+	KEY created_at (created_at)
+) $charset_collate;
+CREATE TABLE $wpdb->awareness (
+	id bigint(20) unsigned NOT NULL auto_increment,
+	room varchar($max_index_length) NOT NULL default '',
+	client_id varchar(32) NOT NULL default '',
+	wp_user_id bigint(20) unsigned NOT NULL default '0',
+	update_value longtext NOT NULL,
+	created_at datetime NOT NULL default '0000-00-00 00:00:00',
+	PRIMARY KEY  (id),
+	UNIQUE KEY room_client (room,client_id),
+	KEY room_created_at (room,created_at),
+	KEY created_at (created_at)
 ) $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 < 61699 ) {
 		upgrade_700();
 	}
 

src/wp-includes/class-wpdb.php

@@ -299,6 +299,8 @@ class wpdb {
 		'term_relationships',
 		'termmeta',
 		'commentmeta',
+		'collaboration',
+		'awareness',
 	);
 
 	/**
@@ -404,6 +406,24 @@ class wpdb {
 	 */
 	public $posts;
 
+	/**
+	 * WordPress Collaboration table.
+	 *
+	 * @since 7.0.0
+	 *
+	 * @var string
+	 */
+	public $collaboration;
+
+	/**
+	 * WordPress Awareness table.
+	 *
+	 * @since 7.0.0
+	 *
+	 * @var string
+	 */
+	public $awareness;
+
 	/**
 	 * WordPress Terms table.
 	 *

src/wp-includes/collaboration.php

@@ -6,6 +6,21 @@
  * @since 7.0.0
  */
 
+/**
+ * Checks whether real-time collaboration is enabled.
+ *
+ * The feature requires both the site option and the database schema
+ * introduced in db_version 61699.
+ *
+ * @since 7.0.0
+ *
+ * @return bool True if collaboration is enabled, false otherwise.
+ */
+function wp_is_collaboration_enabled() {
+	return get_option( 'wp_enable_real_time_collaboration' )
+		&& get_option( 'db_version' ) >= 61699;
+}
+
 /**
  * Injects the real-time collaboration setting into a global variable.
  *
@@ -18,7 +33,7 @@
 function wp_collaboration_inject_setting() {
 	global $pagenow;
 
-	if ( ! get_option( 'wp_enable_real_time_collaboration' ) ) {
+	if ( ! wp_is_collaboration_enabled() ) {
 		return;
 	}
 
@@ -34,3 +49,36 @@ function wp_collaboration_inject_setting() {
 		'after'
 	);
 }
+
+/**
+ * Deletes stale collaboration data from the collaboration table.
+ *
+ * Removes collaboration 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() {
+	if ( ! wp_is_collaboration_enabled() ) {
+		return;
+	}
+
+	global $wpdb;
+
+	// Clean up collaboration rows older than 7 days.
+	$wpdb->query(
+		$wpdb->prepare(
+			"DELETE FROM {$wpdb->collaboration} WHERE created_at < %s",
+			gmdate( 'Y-m-d H:i:s', time() - WEEK_IN_SECONDS )
+		)
+	);
+
+	// Clean up awareness rows older than 60 seconds (2× the 30-second awareness timeout as a buffer).
+	$wpdb->query(
+		$wpdb->prepare(
+			"DELETE FROM {$wpdb->awareness} WHERE created_at < %s",
+			gmdate( 'Y-m-d H:i:s', time() - 60 )
+		)
+	);
+}