docs: def index(self, connection, partition, columns):
          """ Create an index on the columns.
  
          Args:
              connection:
              partition (orm.Partition):
              columns (list of str):
  
          """
          query_tmpl = 'CREATE INDEX ON {table_name} ({column});'
          table_name = '{}_v'.format(partition.vid)
          for column in columns:
              query = query_tmpl.format(table_name=table_name, column=column)
              logger.debug('Creating postgres index.\n    column: {}, query: {}'.format(column, query))
              with connection.cursor() as cursor:
                  cursor.execute(query)
                  cursor.execute('COMMIT;')