code: def push_doc_to_remote(self, remote_name, doc_id=None):
          
          if doc_id is None:
              ret = True
              # @TODO should spawn a thread of each shard...
              for shard in self._shards:
                  if not shard.push_to_remote(remote_name):
                      ret = False
              return ret
          shard = self.get_shard(doc_id)
          return shard.push_to_remote(remote_name)
docs: This will push the master branch to the remote named `remote_name`
          using the mirroring strategy to cut down on locking of the working repo.
  
          `doc_id` is used to determine which shard should be pushed.
          if `doc_id` is None, all shards are pushed.