function wp_upgrade() {
		global $wp_current_db_version, $wp_db_version, $wpdb;

		$wp_current_db_version = __get_option( 'db_version' );

		// We are up-to-date. Nothing to do.
		if ( $wp_db_version == $wp_current_db_version ) {
			return;
		}

		if ( ! is_blog_installed() ) {
			return;
		}

		wp_check_mysql_version();
		wp_cache_flush();
		pre_schema_upgrade();
		make_db_current_silent();
		upgrade_all();
		if ( is_multisite() && is_main_site() ) {
			upgrade_network();
		}
		wp_cache_flush();

		if ( is_multisite() ) {
			$site_id = get_current_blog_id();

			if ( $wpdb->get_row( $wpdb->prepare( "SELECT blog_id FROM {$wpdb->blog_versions} WHERE blog_id = %d", $site_id ) ) ) {
				$wpdb->query( $wpdb->prepare( "UPDATE {$wpdb->blog_versions} SET db_version = %d WHERE blog_id = %d", $wp_db_version, $site_id ) );
			} else {
				$wpdb->query( $wpdb->prepare( "INSERT INTO {$wpdb->blog_versions} ( `blog_id` , `db_version` , `last_updated` ) VALUES ( %d, %d, NOW() );", $site_id, $wp_db_version ) );
			}
		}

		/**
		 * Fires after a site is fully upgraded.
		 *
		 * @since 3.9.0
		 *
		 * @param int $wp_db_version         The new $wp_db_version.
		 * @param int $wp_current_db_version The old (current) $wp_db_version.
		 */
		do_action( 'wp_upgrade', $wp_db_version, $wp_current_db_version );
	}