A question about the pagination example in the guide

I was reading the guide on infinite scrolling pagination where it retrieve progressive more items with

  this.autorun(() => {
      this.getListId(), this.state.get('requestedTodos'));

where this.state.get('requestedTodos') is the number of items to show on client. My question is, does it means that the server needs to read from the database the complete doc set each time the user clicks “loads more”? e.g. The server needs to read from database 10 items, then 20, then 30, … . If so it seems a waste of server resource, even if the mergebox avoid the need to send all items to the client each time. Or is there some optimization that I am unaware of?

Thanks in advance.