Adding Robustness in Dynamic Preemptive Scheduling

In this paper we introduce a robust earliest deadline scheduling algorithm for deal ing with hard aperiodic tasks under overloads in a dynamic realtime environment The algorithm synergistically combines many features including dynamic guarantees graceful degradation in overloads deadline tolerance resource reclaiming and dy namic reguarantees A necessary and sucient schedulability test is presented and an ecient On guarantee algorithm is proposed The new algorithm is evaluated via simulation and compared to several baseline algorithms The experimental results show excellent performance of the new algorithm in normal and overload conditions Static realtime systems are designed for worst case situations Assuming that all the assumptions made in the design and analysis are correct we can say that the level of guarantee for these systems is absolute and all tasks will make their deadlines Unfortunately static systems are not always possible becaus

Integrating standard transactions in firm real-time database systems

Real-time database systems are designed to handle workloads where transactions have completion deadlines and the goal is to meet these deadlines. However, many real-time database environments are characterized by workloads that are a mix of real-time and standard (non-real-time) transactions. Unfortunately, the system policies used to meet the performance goals of real-time transactions often work poorly for standard transactions. In particular, optimistic concurrency control algorithms are recommended for real-time transactions, whereas locking-based protocols are suited for standard transactions. In this paper, we present a new database system architecture in which realtime transactions use optimistic concurrency control and, simultaneously, standard transactions use locking. We prove that our architecture maintains data integrity and show, through a simulation study, that it provides significantly improved performance for the standard transactions without diminishing the real-time transaction performance. We also show, more generally, that the proposed architecture correctly supports the co-existence of any group of concurrency control algorithms that adhere to a standard interface

MIRROR: a state-conscious concurrency control protocol for replicated real-time databases

Data replication can help database systems meet the stringent temporal constraints of current real-time applications, especially Web-based directory and electronic commerce services. A prerequisite for realizing the benefits of replication, however, is the development of high-performance concurrency control mechanisms. In this paper, we present managing isolation in replicated real-time object repositories (MIRROR), a concurrency control protocol specifically designed for firm-deadline applications operating on replicated real-time databases. MIRROR augments the classical O2PL concurrency control protocol with a novel state-based real-time conflict resolution mechanism. In this scheme, the choice of conflict resolution method is a dynamic function of the states of the distributed transactions involved in the conflict. A feature of the design is that acquiring the state knowledge does not require inter-site communication or synchronization, nor does it require modifications to the two-phase commit protocol. Using a detailed simulation model, we compare MIRROR's performance against the real-time versions of a representative set of classical replica concurrency control protocols for a range of transaction workloads and system configurations. Our performance studies show that (a) the relative performance characteristics of these protocols in the real-time environment can be significantly different from their performance in a traditional (non-real-time) database system, (b) MIRROR provides the best performance in both fully and partially replicated environments for real-time applications with low to moderate update frequencies, and (c) MIRROR's simple to implement conflict resolution mechanism works almost as well as more sophisticated strategies. (C) 2002 Elsevier Science Ltd. All rights reserved

Collusion-Resistant Processing of SQL Range Predicates

Prior solutions for securely handling SQL range predicates in outsourced Cloud-resident databases have primarily focused on passive attacks in the Honest-but-Curious adversarial model, where the server is only permitted to observe the encrypted query processing. We consider here a significantly more powerful adversary, wherein the server can launch an active attack by clandestinely issuing specific range queries via collusion with a few compromised clients. The security requirement in this environment is that data values from a plaintext domain of size N should not be leaked to within an interval of size H. Unfortunately, all prior encryption schemes for range predicate evaluation are easily breached with only O(log 2 �) range queries, where �= N/ H. To address this lacuna, we present SPLIT, a new encryption scheme where the adversary requires exponentially more�O(�) �range queries to breach the interval constraint and can therefore be easily detected by standard auditing mechanisms. The novel aspect of SPLIT is that each value appearing in a range-sensitive column is first segmented into two parts. These segmented parts are then independently encrypted using a layered composition of a secure block cipher with the order-preserving encryption and prefix-preserving encryption schemes, and the resulting ciphertexts are stored in separate tables. At query processing time, range predicates are rewritten into an equivalent set of table-specific sub-range predicates, and the disjoint union of their results forms the query answer. A detailed evaluation of SPLIT on benchmark database queries indicates that its execution times are well within a factor of two of the corresponding plaintext times, testifying its efficiency in resisting active adversaries. © 2018, The Author(s)

Scheduling Access To Temporal Data In Real-Time Databases

INTRODUCTION A real-time database system is a transaction processing system designed to handle workloads in which transactions have deadlines. However, many realworld applications involve not only transactions with time constraints, but also data with time constraints. Such data, typically obtained from sensors, become inaccurate with the passage of time. Examples of such applications include autopilot systems, robot navigation, and program stock trading [14]. While considerable work has been done on real-time databases, most of it assumes that only transactions have deadlines [1, 7]. New solutions that consider data time constraints are required for both concurrency control and cpu scheduling. In this chapter, new solutions are presented based on data-deadlines and time cognizant forced wait policies. Informally, data-deadline can be viewed as the deadline that a transaction implicitly gets due to the temporal constraints of the data accessed by the transaction. When a trans

Adding Robustness in Dynamic Preemptive Scheduling

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