code: def update_checkpoint(self, checkpoint):
          
          if checkpoint is not None and checkpoint != self.checkpoint:
              self.checkpoint = checkpoint
              with self.oplog_progress as oplog_prog:
                  oplog_dict = oplog_prog.get_dict()
                  # If we have the repr of our oplog collection
                  # in the dictionary, remove it and replace it
                  # with our replica set name.
                  # This allows an easy upgrade path from mongo-connector 2.3.
                  # For an explanation of the format change, see the comment in
                  # read_last_checkpoint.
                  oplog_dict.pop(str(self.oplog), None)
                  oplog_dict[self.replset_name] = checkpoint
                  LOG.debug("OplogThread: oplog checkpoint updated to %s", checkpoint)
          else:
              LOG.debug("OplogThread: no checkpoint to update.")
docs: Store the current checkpoint in the oplog progress dictionary.