Collaboration: Add composite index for awareness room+created_at query

The awareness SELECT filters on WHERE room = %s AND created_at >= %s.
The existing UNIQUE KEY room_client covers room but not created_at,
requiring a row filter after the index lookup.

Adds KEY room_created_at (room, created_at) so both conditions are
satisfied directly from the index. The existing KEY created_at is
retained for cron cleanup queries that filter on created_at alone.

Bumps db_version to 61835.

Author: josephfusco

src/wp-admin/includes/schema.php

@@ -205,6 +205,7 @@ function wp_get_db_schema( $scope = 'all', $blog_id = 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";
 

src/wp-includes/version.php

@@ -23,7 +23,7 @@
  *
  * @global int $wp_db_version
  */
-$wp_db_version = 61834;
+$wp_db_version = 61835;
 
 /**
  * Holds the TinyMCE version.