Protocols for consistent data broadcast and cache management in mobile computing systems

Abstract

This dissertation studies the data inconsistency and stale data problem in data broadcast to mobile transactions. If the update transactions are executed while data items are being broadcast without any control, the transactions generated by mobile clients may observe inconsistent data values. In addition, many consistent broadcast schedulers distribute stale data which is much less useful to mobile clients. In this thesis, a new protocol called Ordered-Update-First with Order (OUFO) is proposed for concurrency control between read-only, ordered mobile transactions and update transactions. OUFO is demonstrated to offer superior performances to the well known Multiple Version protocol in most aspects; it can also be applied easily to different broadcast systems. To reduce the size of invalidation reports, another protocol called OUFO+IAVI is proposed. This protocol combines the strength of OUFO and the Invalidation by Absolute Validity Interval protocol to reduce the broadcast overhead especially for mobile systems whose update rate for data items is high. The third protocol proposed in this thesis is the Hybrid Real Time Multi-Version (MV+LVO+AR) protocol which is an improved version of the MV protocol. MV+LVO+AR aims at maximizing data currency, minimizing transaction aborted and providing consistent data items, which are important performance objectives of a time-constrained computing system. To improve system performance, a prioritized on-demand broadcast scheme is combined with data broadcast schemes to disseminate data items to the mobile transactions in order to minimize the deadline missing probability of the transactions and the resulting scheme evaluated based on extensive simulation studies.