# Unable  to  generate serial numbers concurrently 

class SequenceMixin()

    def _get_last_sequence(self, relaxed=False, with_prefix=None):	​...​
       query = """
    	​	​UPDATE {table} SET write_date = write_date WHERE id = (
        	​	​SELECT id FROM {table}
        	​	​{where_string}
        	​	​AND sequence_prefix = (SELECT sequence_prefix FROM {table} {where_string} ORDER BY id DESC LIMIT 1)
        	​	​ORDER BY sequence_number DESC
        	​	​LIMIT 1
    	​	​)
    		​​RETURNING {field};
	​	​""".format(
    	​table=self._table,
   	​ 	​where_string=where_string,
    	​field=self._sequence_field,
	​	​)
   
    ...

​