The Watch Doc service can be used to upload (large) text files into a mirror table. It uploads through an http(s) web request.
ServerJS parses the file and executes insert SQL statements
By following the tutorial, you will be able to import 50.000 contacts/records in a mirror table in less than 3 minutes.
The Watch Doc was not really intended for this, very inventive :).
The nice thing is that you can drop a file and the data gets loaded into the mirror table.