code: func (s *Session) SetBatch(n int) {
  	if n == 1 {
  		// Server interprets 1 as -1 and closes the cursor (!?)
  		n = 2
  	}
  	s.m.Lock()
  	s.queryConfig.op.limit = int32(n)
  	s.m.Unlock()
  }
docs: // SetBatch sets the default batch size used when fetching documents from the
  // database. It's possible to change this setting on a per-query basis as
  // well, using the Query.Batch method.
  //
  // The default batch size is defined by the database itself.  As of this
  // writing, MongoDB will use an initial size of min(100 docs, 4MB) on the
  // first batch, and 4MB on remaining ones.