Execute the KEYS command on all Redis shards.

        Args:
            pattern: The KEYS pattern to query.

        Returns:
            The concatenated list of results from all shards.

def _keys(self, pattern):
        """Execute the KEYS command on all Redis shards.

        Args:
            pattern: The KEYS pattern to query.

        Returns:
            The concatenated list of results from all shards.
        """
        result = []
        for client in self.redis_clients:
            result.extend(list(client.scan_iter(match=pattern)))
        return result