. In data broadcast environments, the limited bandwidth of the upstream communication channel from the mobile clients to the server bars the application of conventional concurrency control protocols. In this paper, we propose a new variant of the optimistic concurrency control protocol that is suitable for the broadcast environments. In this protocol, read-only mobile transactions can be processed locally at the mobile clients. Only update transactions are sent to the server for final validation. These update transactions will have a better chance of commitment because they have gone through partial validation at the mobile clients. This protocol, while using less control information to process transactions at the mobile clients, provides autonomy between the mobile clients and the server with minimum upstream communication, which are desirable features to the scalability of applications running in broadcast environments. 1 Introduction Data broadcast environments pose a...

Although data broadcast has been shown to be an efficient method for disseminating data items in mobile computing systems, the issue on how to ensure consistency and currency of data items provided to mobile transactions (MT), which are generated by mobile clients, has not been examined adequately. While data items are being broadcast, update transactions may install new values for them. If the executions of update transactions and the broadcast of data items are interleaved without any control, mobile transactions may observe inconsistent data values. The problem will be more complex if the mobile clients maintain some cached data items for their mobile transactions. In this paper, we propose a concurrency control method, called Ordered Update First with Order (OUFO), for the mobile computing systems where a mobile transaction consists of a sequence of read operations and each MT is associated with a time constraint on its completion time. Besides ensuring data consistency and maximizing currency of data to mobile transactions, OUFO also aims at reducing data access delay of mobile transactions using client caches. A hybrid rebroadcast/invalidation report mechanism is designed in OUFO for checking validity of cached data items so as to improve cache consistency and minimize the overhead of transaction restarts due to data conflicts. This is highly important to the performance of the mobile computing systems where the mobile transactions are associated with a deadline constraint on their completion times. Extensive simulation experiments have been performed to compare the performance of OUFO with two other efficient schemes, the multi-version broadcast method (MV) and the periodic invalidation report method (IR). The performance results show that OUFO offers better pe...

Observing that it is impractical to use traditional methods to control concurrency in broadcast-based asymmetric communication environment, we introduce a concurrency control protocol designed for broadcast-based transaction processing called STUBcast (Server Timestamp and Update Broadcast Supported Concurrency). STUBcast supports two new correctness criteria proposed in this paper - Single Serializability and Local Serializability. These criteria are weaker than global serializability but are practical and easier to achieve in broadcast environment. This article also shows some simulation results. These results suggest that STUBcast could be very efficient in realistic application environment.

In this paper, we study the data dissemination problem in time-constrained mobile computing systems (TCMCS) in which maximizing data currency (minimizing staleness) and meeting transaction deadlines are of equal importance as providing consistent data items to transactions. We first investigate what are the performance problems of the multi-version data (MV) broadcast technique when it is used for TCMCS. Then, we propose various enhancements to resolve the problems. In order to further reduce the probability of missing deadlines, we introduce a prioritized on-demand broadcast scheme, which is integrated with the data broadcast mechanism for disseminating data items to time-constrained transactions. The performance characteristics of the proposed strategies have been studied through extensive simulation.

Observing that it is impractical to use traditional methods to control concurrency for transaction processing in broadcast-based asymmetric communication environment, this paper introduces a concurrency control protocol designed for broadcast-based transaction processing called STUBcast (Server Timestamp and Update Broadcast Supported Concurrency). It then focuses on the correctness proof of STUBcast on supporting two new proposed correctness criteria, Single Serializability and Local Serializability, which are weaker than global serializability but are practical in broadcast environment.

Although data broadcast has been shown to be an efficient method for disseminating data items in a mobile computing system with large number of clients, the issue on how to ensure the data consistency observed by mobile transactions, which are generated by mobile clients, has been largely ignored by researchers in the area. While data items are being broadcast, update transactions may install new values for the data items. If the executions of updates and broadcast of data items are interleaved without any control, the mobile transactions may observe inconsistent data values. In this paper, we propose a serialization checking method (SCM) for concurrency control between read-only mobile transactions and update transactions. SCM is based on the framework of an earlier algorithm, Update First with Ordering (UFO), but improves on that algorithm by reducing re-broadcast overhead when the probability of data conflict between updates and data broadcast is high. Simulation experiments have been performed to investigate the performance characteristics of the proposed method.

With the inclusion of actuation capabilities, emerging wireless sensor applications are much less tolerant to inconsistencies in decisions compared to passive sensing applications. Multi-hop networks suffer from these problems more profoundly as they cannot directly utilize atomic broadcast operations for coordination. In this study, we provide a lightweight single hop primitive, Read-All-Write-Self (RAWS), that achieves optimistic concurrency control. RAWS guarantees serializability, which simplifies implementation and verification of distributed algorithms, compared to the low level message passing model. We also present a self-stabilizing multi-hop extension of RAWS, called Multi-hop Optimistic Concurrency Control Algorithm (MOCCA), to address the challenges of multi-hop networks. MOCCA improves the performance of RAWS transactions in multi-hop networks while maintaining serializability. We implement MOCCA in JProwler simulator using TDMA- and CSMA-based MAC layers and compare it against a lightweight locking scheme and serial execution of transactions. Our results indicate that concurrent execution in MOCCA can outperform serial execution in task completion time via better utilization of broadcasts and concurrent execution. Finally, we also show that under heavy loads optimistic concurrency control provides much better performance compared to locking schemes.

In the wireless environment, dissemination techniques may improve data access for the users. In this paper, we show a description of dissemination architecture that fits the overall telecommunication network. This architecture is designed to provide efficient data access and power saving for the mobile units. A concurrency control approach, MCD, is suggested for data consistency and conflict checking. A performance study shows that the power consumption, space overhead, and response time associated with MCD is far less than other previous techniques.