Broadcasting consistent data to read-only transactions from mobile clients

In this paper, we study the data inconsistency problem in data-broadcast-to-mobile transactions. While data items in a mobile computing system are being broadcast, update transactions may install new values for the data items. If the executions of update transactions and broadcast of data items are interleaved without any control, the transactions generated by mobile clients, called mobile transactions, may observe inconsistent data values. In this paper we propose a new protocol, called Update-first with Order (UFO), for concurrency control between read-only mobile transactions and update transactions. We show that although the protocol is simple, all the schedules are serializable when the UFO protocol is applied. Furthermore, the new protocol possesses many desirable properties for mobile computing systems such as the mobile transactions do not need to set any lock before they read a data item from the 'air' and the protocol can be applied to different broadcast algorithms. Its performance has been investigated with extensive simulation experiments. The results show that the protocol can maximize the freshness of the data items provided to mobile transactions and the broadcast overhead is not heavy especially when the arrival rate of the update transactions is not very high.