Random curious question. I was pondering the kanban backend. How do you store the order of the kanban cards in your database and keep that in sync with what's in the UI?
So, if I move the 3rd card to the 2nd position, its “pos” becomes 1500. This means it doesn’t have to constantly renumber the cards -- but, every once and a while, the server does reorder the “pos” fields for a whole list and send the new values down the socket.
Order is stored to sort field as number. When changing order with JQuery Draggable/Droppable/Sortable, it saves new order to browserside MiniMongo, that is made with Javascript, and then to serverside MongoDB. It is possible use mouse or touchscreen to drag drop reorder board icons at All Boards page, swimlanes, lists, cards and checklists. There are also roles at right sidebar avatar icons popup settings, so BoardAdmin can drag drop everything, and there are some limits for other roles, like Normal, CommentOnly etc https://news.ycombinator.com/item?id=44165257
For realtime updates, Meteor web framework reads realtime changes from MongoDB OpLog (operations log), and with Publish/Subscribe at realtime updates all changes immediately for all users, like what card moved, etc.
There is in progress of adding support for other databases, like SQLite etc.