Items/Records re-ordering?

Items/Records re-ordering?

Assume that on a multiple-user application that the same request may be
initiated by multiple users at the same time, which these requests at the
end will be some ajax calls to some server-side action we have a routine
executed by that action/method on server as below:
routine task : it is responsible to do the reordering such that, imagine
items are not connected to each other, there is no doubly linked-list data
structure in place but all items have an assumed ordering by default and
represented to users by that order, when an add item , or delete item , or
update item operation is initiated by those ajax calls, ordering will be
different as the entry is like FIFO.
currently I need to update all the records, orderNumber column to keep
track of all the changed, On an update operation because items are movable
in the user interface and users have the facility of a drag and drop
interaction, items can go up or down the original ordered list and change
those orderings.
what would you suggest as the most efficient method for keeping track of
these ordering changes in which will have the least performance cost on
server as well as keeping an acceptable user interaction for users?
Development Platform is ASP.NET MVC4 , Persistence using SQL Server