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The design and implementation of an adaptive Web server architecture are presented to provide relative and absolute connection delay guarantees for different service classes. The adaptive architecture based on feedback control loops and the theoretic techniques used to suitably model and design the feedback loops are described, and experimental results demonstrate that the adaptive server provides robust delay guarantees even when workload varies significantly.

A spatiotemporal communication protocol for sensor networks called SPEED is presented. End-to-end soft real-time communication is achieved by maintaining a desired delivery speed across the sensor network through a novel combination of feedback control and nondeterministic geographic forwarding.

The demand for real-time data services is increasing in many applications including e-commerce, agile manufacturing, and telecommunications network management. In these applications, it is desirable to execute transactions within their deadlines, i.e., before the real-world status changes, using fresh (temporally consistent) data. However, meeting these fundamental requirements is challenging due to dynamic workloads and data access patterns in these applications. Further, transaction timeliness and data freshness requirements may conflict. In this paper, we define average/transient deadline miss ratio and new data freshness metrics to let a database administrator specify the desired quality of real-time data services for a specific application. We also present a novel QoS management architecture for real-time databases to support the desired QoS even in the presence of unpredictable workloads and access patterns. To prevent overload and support the desired QoS, the presented architecture applies feedback control, admission control, and flexible freshness management schemes. A simulation study shows that our QoS-aware approach can achieve a near zero miss ratio and perfect freshness, meeting basic requirements for real-time transaction processing. In contrast, baseline approaches fail to support the desired miss ratio and/or freshness in the presence of unpredictable workloads and data access patterns. Index Terms--Real-time database, deadline miss ratio, sensor data freshness, QoS management.

In this paper, issues involved in the design of a real-time database which maintains data temporal consistency are discussed. The concept of data-deadline is introduced and time cognizant transaction scheduling policies are proposed. Informally, data-deadline is a deadline assigned to a transaction due to the temporal constraints of the data accessed by the transaction. Further, two time cognizant forced wait policies which improve performance significantly by forcing a transaction to delay further execution until a new version of sensor data becomes available are proposed. A way to exploit temporal data similarity to improve performance is also proposed. Finally, these policies are evaluated through detailed simulation experiments. The simulation results show that taking advantage of temporal data semantics in transaction scheduling can significantly improve the performance of user transactions in real-time database systems. In particular, it is demonstrated that under the forced wait policy, the performance can be improved significantly. Further improvements result by exploiting data similarity. Index Terms--Real-time database systems, temporal consistency, earliest deadline first, least slack first, data-deadline, transaction processing.

1. INTRODUCTION Real-time computing is an enabling technology for many important application areas, including process control, nuclear power plants, agile manufacturing, intelligent vehicle highway systems, avionics, air-traffic control, telecommunications (the [...]

Basic Reclaiming and Reclaiming with Early Start, two resource reclaiming algorithms, are correct and simple. Both these algorithms have been implemented to demonstrate that the algorithms are applicable in the Spring Kernel. Resource reclaiming is very important and very effective in dynamic real time multiprocessor environments.

Research was conducted to examine the design of the UMass Spring threads package and its implementation and measurement on a representative platform. The threads package has a high-level design and unique semantics that is well suited for hard real-time environments. Additional performance improvements that include reduced context switching overhead and reduced average-case memory access durations arise from the adoption of the threads package in the UMass Spring kernel.

This paper, presents a modified priority based probe algorithm for deadlock detection and resolution in distributed database systems. The original priority based probe algorithm was presented by Sinha and Natarajan based on work by Chandy, Misra, and Haas. Various examples are used to show that the original priority based algorithm either fails to detect deadlocks or reports deadlocks which do not exist in many situations. A modified algorithm which eliminates these problems is proposed. This algorithm has been tested through simulation and appears to be error free. Finally, the performance of the modified algorithm is briefly discussed. [ABSTRACT FROM AUTHOR]