public function convert_reply_to_parents( $start = 1 ) {
		$has_update = false;
		$query      = ! empty( $this->sync_table )
			? $this->wpdb->prepare( "SELECT value_id, meta_value FROM {$this->sync_table_name} WHERE meta_key = %s AND meta_value > 0 LIMIT {$start}, {$this->max_rows}",           '_bbp_old_reply_to_id' )
			: $this->wpdb->prepare( "SELECT post_id AS value_id, meta_value FROM {$this->wpdb->postmeta} WHERE meta_key = %s AND meta_value > 0 LIMIT {$start}, {$this->max_rows}", '_bbp_old_reply_to_id' );

		foreach ( $this->count_rows_by_results( $query ) as $row ) {
			$reply_to = $this->callback_reply_to( $row->meta_value );
			$this->query( $this->wpdb->prepare( "UPDATE {$this->wpdb->postmeta} SET meta_value = %s WHERE meta_key = %s AND post_id = %d LIMIT 1", $reply_to, '_bbp_reply_to', $row->value_id ) );
			$has_update = true;
		}

		return ! $has_update;
	}