code: func (q *Query) SetMaxScan(n int) *Query {
  	q.m.Lock()
  	q.op.options.MaxScan = n
  	q.op.hasOptions = true
  	q.m.Unlock()
  	return q
  }
docs: // SetMaxScan constrains the query to stop after scanning the specified
  // number of documents.
  //
  // This modifier is generally used to prevent potentially long running
  // queries from disrupting performance by scanning through too much data.