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Sheung-lun Hung - One of the best experts on this subject based on the ideXlab platform.
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A Priority ceiling protocol with dynamic adjustment of serialization order
Proceedings 13th International Conference on Data Engineering, 1997Co-Authors: Sheung-lun HungAbstract:The difficulties of providing a guarantee of meeting transaction deadlines in hard real-time database systems lie in the problems of Priority Inversion and of deadlocks. Priority Inversion and deadlock problems ensue when concurrency control protocols are adapted in Priority-driven scheduling. The blocking delay due to Priority Inversion can be unbounded, which is unacceptable in the mission-critical real-time applications. Some Priority ceiling protocols have been proposed to tackle these two problems. However, they are too conservative in scheduling transactions for the single-blocking and deadlock-free properties, leading to many unnecessary transaction blockings. The authors analyze the unnecessary transaction blocking problem inherent in these Priority ceiling protocols and investigate the conditions for allowing a higher Priority transaction to preempt a lower Priority transaction using the notion of dynamic adjustment of serialization order. A new Priority ceiling protocol is proposed to solve the unnecessary blocking problem, thus enhancing schedulability. They also devise the worst-case schedulability analysis for the new protocol which provides a better schedulability condition than other protocols.
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ICDE - A Priority ceiling protocol with dynamic adjustment of serialization order
Proceedings 13th International Conference on Data Engineering, 1997Co-Authors: Sheung-lun HungAbstract:The difficulties of providing a guarantee of meeting transaction deadlines in hard real-time database systems lie in the problems of Priority Inversion and of deadlocks. Priority Inversion and deadlock problems ensue when concurrency control protocols are adapted in Priority-driven scheduling. The blocking delay due to Priority Inversion can be unbounded, which is unacceptable in the mission-critical real-time applications. Some Priority ceiling protocols have been proposed to tackle these two problems. However, they are too conservative in scheduling transactions for the single-blocking and deadlock-free properties, leading to many unnecessary transaction blockings. The authors analyze the unnecessary transaction blocking problem inherent in these Priority ceiling protocols and investigate the conditions for allowing a higher Priority transaction to preempt a lower Priority transaction using the notion of dynamic adjustment of serialization order. A new Priority ceiling protocol is proposed to solve the unnecessary blocking problem, thus enhancing schedulability. They also devise the worst-case schedulability analysis for the new protocol which provides a better schedulability condition than other protocols.
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Integrated concurrency control protocol for hard real-time database systems
IEE Proceedings - Computers and Digital Techniques, 1997Co-Authors: Sheung-lun HungAbstract:Real-time transactions must meet their deadlines in hard real-time database systems (RTDBS). To preserve data integrity, hard RTDBS require concurrency control protocols to synchronise transactions to access shared data. Transaction blocking enforced by concurrency control protocols leads to Priority Inversion problems which violate the principle of Priority-based scheduling and degrade system schedulability. Unfortunately, this blocking time can be indefinitely long, which is unacceptable in hard real-time applications. An integrated scheduling and concurrency control protocol is proposed that allows a high Priority transaction to pre-empt an uncommitted lower Priority transaction while preventing the lower Priority transaction from being restarted even in the face of data conflicts. The new protocol alleviates Priority Inversion problems by allowing more transaction schedules than other protocols.
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RTCSA - A pre-emptive transaction scheduling protocol for controlling Priority Inversion
Proceedings of 3rd International Workshop on Real-Time Computing Systems and Applications, 1996Co-Authors: Sheung-lun HungAbstract:Hard real-time database systems (RTDBS) must provide a guarantee that real-time transactions meet their deadlines. To preserve data consistency, hard RTDBS require concurrency control protocols to synchronize transactions to access the shared data. Transaction blocking enforced by concurrency control protocols leads to the Priority Inversion problem that violates the principle of Priority-based scheduling and degrades system schedulability. Moreover, this blocking delay due to Priority Inversion can be unbounded, which is unacceptable in hard real-time applications. Some Priority ceiling protocols have been proposed to control Priority Inversion. However, they suffer from the problem of unnecessary transaction blockings due to their conservatism of scheduling transactions to access the shared data. We propose a new transaction scheduling protocol that exploits the semantics of transaction operations to enhance transaction preemptability. It can avoid some unnecessary transaction blockings and provide better worst-case scheduling conditions for a transaction set compared to other protocols.
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A pre-emptive transaction scheduling protocol for controlling Priority Inversion
Proceedings of 3rd International Workshop on Real-Time Computing Systems and Applications, 1996Co-Authors: Sheung-lun HungAbstract:Hard real-time database systems (RTDBS) must provide a guarantee that real-time transactions meet their deadlines. To preserve data consistency, hard RTDBS require concurrency control protocols to synchronize transactions to access the shared data. Transaction blocking enforced by concurrency control protocols leads to the Priority Inversion problem that violates the principle of Priority-based scheduling and degrades system schedulability. Moreover, this blocking delay due to Priority Inversion can be unbounded, which is unacceptable in hard real-time applications. Some Priority ceiling protocols have been proposed to control Priority Inversion. However, they suffer from the problem of unnecessary transaction blockings due to their conservatism of scheduling transactions to access the shared data. We propose a new transaction scheduling protocol that exploits the semantics of transaction operations to enhance transaction preemptability. It can avoid some unnecessary transaction blockings and provide better worst-case scheduling conditions for a transaction set compared to other protocols.
H. Tokuda - One of the best experts on this subject based on the ideXlab platform.
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RTSS - Integrated management of Priority Inversion in Real-Time Mach
1993 Proceedings Real-Time Systems Symposium, 1993Co-Authors: T. Nakajima, T. Kitayama, H. Arakawa, H. TokudaAbstract:Synchronization and communication are two common sources of Priority Inversion which may make the behavior of systems unpredictable and unanalyzable. In microkernel-based systems, they are heavily used for building operating system servers and decomposing applications into several tasks. The management of priorities in IPC and synchronization should be integrated using a uniform mechanism since Priority Inversion occurs if such integration is not supported. Also, a highly preemptable server structure should be provided because the execution in a server may take up too much time. We propose an integrated real-time resource management model, and a real-time server model which solve the above problems. We implemented and evaluated the models in Real-Time Mach using a uniform mechanism. Our approach enables us to build operating system servers and to decompose applications into several tasks without incurring Priority Inversion. >
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USENIX Microkernels and Other Kernel Architectures Symposium - RT-IPC: an IPC extension for real-time mach
1993Co-Authors: Takuro Kitayama, H. Tokuda, T. NakajimaAbstract:Interprocess communication (IPC) provides the fundamental mechanism for the Mach microkernel to be extensible and flexible. Mach IPC provides efficient communication mechanisms for many applications. However, it does not provide sufficient functionality for real-time applications which have rigid timing constraints among threads. In Real-Time Mach (RT-Mach), we have extended Mach IPC to be Priority Inversion free for real-time applications. This paper describes the Real-Time IPC (RT-IPC) facilities, its implementation, and the evaluation results. We used the Distributed Hartstone (DHS) real-time benchmark for the evaluation and the results show that RT-IPC can reduce Priority Inversion and improve CPU utilization for real-time applications.
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Integrated management of Priority Inversion in Real-Time Mach
1993 Proceedings Real-Time Systems Symposium, 1993Co-Authors: T. Nakajima, T. Kitayama, H. Arakawa, H. TokudaAbstract:Synchronization and communication are two common sources of Priority Inversion which may make the behavior of systems unpredictable and unanalyzable. In microkernel-based systems, they are heavily used for building operating system servers and decomposing applications into several tasks. The management of priorities in IPC and synchronization should be integrated using a uniform mechanism since Priority Inversion occurs if such integration is not supported. Also, a highly preemptable server structure should be provided because the execution in a server may take up too much time. We propose an integrated real-time resource management model, and a real-time server model which solve the above problems. We implemented and evaluated the models in Real-Time Mach using a uniform mechanism. Our approach enables us to build operating system servers and to decompose applications into several tasks without incurring Priority Inversion.
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NOSSDAV - Priority Consistency in Protocol Architecture
Network and Operating System Support for Digital Audio and Video, 1992Co-Authors: C.w. Mercer, H. TokudaAbstract:The protocol processing software of a multimedia operating system must provide fast response time and predictable delays for time-constrained data streams like digital audio and video streams. This paper describes several different techniques for scheduling the protocol processing of messages. These techniques are analyzed and their (simulated) performance compared using various metrics. One of these metrics is the Priority Inversion factor which provides a way of quantifying Priority Inversion in the system. Protocol processing time and context switch time are given as parameters in the simulations, and we present guidelines for choosing between the message scheduling techniques based on the ratio of protocol processing time to context switch time for a given system.
Udai Shanker - One of the best experts on this subject based on the ideXlab platform.
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RACE: A Concurrency Control Protocol for Time-Constrained Transactions
Arabian Journal for Science and Engineering, 2020Co-Authors: Sarvesh Pandey, Udai ShankerAbstract:The two-phase locking with high Priority (2PL-HP) protocol is a broadly used concurrency control protocol as it better handles the Priority Inversion problem. However, its performance might get degraded due to the inclusion of cyclic restart, deadlock, unnecessary abort, pseudo-Priority Inversion, and starvation. To overcome the above problems, this paper proposes a R eduction of long transactions starvation effect, A voidance of deadlock and pseudo-Priority Inversion, and C onditional-restart for an E fficient resource utilization (RACE) concurrency control protocol. The RACE specifically aims at reducing the transaction miss percent by eliminating the following problems—deadlock through dividing the execution stage in the locking phase and processing phase, the cyclic restart through prejudging its occurrence, and the pseudo-Priority Inversion that may occur with an intermediate lock holder low Priority cohort. Moreover, it reduces unnecessary transaction aborts through the utilization of the Priority inheritance method and saves long transactions from being starved to some extent by ensuring fair chances of their completion. Simulation results confirm up to 11% improvement in transactions miss percent and up to 38% reduction in transactions’ rollbacks in RACE protocol over 2PL-HP and extended 2PL-HP.
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Causes, Effects, and Consequences of Priority Inversion in Transaction Processing
Handling Priority Inversion in Time-Constrained Distributed Databases, 2020Co-Authors: Sarvesh Pandey, Udai ShankerAbstract:The problem of Priority Inversion occurs when a high Priority task is required to wait for completion of some other task with low Priority as a result of conflict in accessing the shared system resource(s). This problem is discussed by many researchers covering a wide range of research areas. Some of the key research areas are real-time operating systems, real-time systems, real-time databases, and distributed real-time databases. Irrespective of the application area, however, the problem lies with the fact that Priority Inversion can only be controlled with no method available to eliminate it entirely. In this chapter, the Priority Inversion-related scheduling issues and research efforts in this direction are discussed. Different approaches and their effectiveness to resolve this problem are analytically compared. Finally, major research accomplishments to date have been summarized and several unanswered research questions have also been listed.
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transaction scheduling protocols for controlling Priority Inversion a review
Computer Science Review, 2020Co-Authors: Sarvesh Pandey, Udai ShankerAbstract:Abstract In advanced real-time distributed computing databases, the main performance criterion is to reduce the ‘deadline miss’ by the transactions; of course, consistency constraints also need to be satisfied. The goal of these applications is not to provide simply real-time transaction execution, but rather to provide a highly predictable, analysable, schedulable and reliable distributed computing platform to the users. The problem of resource conflicts amongst distributed real-time transactions and their handlings through various Priority scheduling protocols highly affect the performance of the underlying applications. The past research works were mostly restricted to extend the traditional transaction processing techniques to resolve the issue of conflicts, and thus to improve the performance. The last review paper, largely on this issue, appeared in Shanker et al. (2008) [1] ; since then many noteworthy algorithms have been described in the literature. Till date, no study was found discussing transaction processing techniques with data conflict issue in focus. Hence, our objective is to comprehensively discuss the state-of-the-art transaction scheduling protocols with an emphasis on the handling of execute–execute & execute–commit conflicts, and real-time optimistic concurrency control (OCC) protocols. The strengths and weaknesses of existing approaches are also discussed.
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Priority Inversion in drtdbs challenges and resolutions
International Conference Data Science and Management, 2018Co-Authors: Sarvesh Pandey, Udai ShankerAbstract:The primary 1 performance objective in distributed real-time database systems (DRTDBS) is to minimize the number of transactions missing their deadlines. Demanding nature of this objective makes traditional approaches and even existing approaches inadequate. The past researches have been mostly devoted to outspreading traditional transaction processing methods to resolve the issues. However, for the design of DRTDBS, new policies/protocols must be designed to resourcefully handle the concurrent execution of transactions. Our aim is to develop new concurrency control protocols, commit protocols and to compare their performance with existing protocols. Another plan is to extend our work to nested transaction model, replication environment and possibly mobile environment.
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COMAD/CODS - Priority Inversion in DRTDBS: challenges and resolutions
Proceedings of the ACM India Joint International Conference on Data Science and Management of Data - CoDS-COMAD '18, 2018Co-Authors: Sarvesh Pandey, Udai ShankerAbstract:The primary 1 performance objective in distributed real-time database systems (DRTDBS) is to minimize the number of transactions missing their deadlines. Demanding nature of this objective makes traditional approaches and even existing approaches inadequate. The past researches have been mostly devoted to outspreading traditional transaction processing methods to resolve the issues. However, for the design of DRTDBS, new policies/protocols must be designed to resourcefully handle the concurrent execution of transactions. Our aim is to develop new concurrency control protocols, commit protocols and to compare their performance with existing protocols. Another plan is to extend our work to nested transaction model, replication environment and possibly mobile environment.
Xibo Wang - One of the best experts on this subject based on the ideXlab platform.
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several methods of design and implementation to solve Priority Inversion problem in uc os ii
International Conference on Intelligent Networks and Intelligent Systems, 2013Co-Authors: Xibo Wang, Zhongling YangAbstract:Multi-task concurrent execution and resource sharing based on preemptive scheduling strategy may cause Priority Inversion phenomenon in real-time systems. Priority Inversion phenomenon is the significant reason of unpredictable errors in real-time system, serious continuous Priority Inversion phenomenon will lead to real-time system collapse. The paper analyzes the phenomenon and the cause of the phenomenon, puts forward several design and implementation methods to solve Priority Inversion problem suitable for various application scenarios in μC/OS-II. A Priority exchange method is proposed to improve Priority inheritance protocol. The proposed method limit Priority Inversion phenomenon to one level. Theoretical analyses and experimental results indicate that the methods to solve the Priority Inversion problem in μC/OS-II are concise and effective, provides reasonable technical means for the safe running of complex real-time applications in μC/OS-II.
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Several Methods of Design and Implementation to Solve Priority Inversion Problem in uC/OS-II
2013 6th International Conference on Intelligent Networks and Intelligent Systems (ICINIS), 2013Co-Authors: Xibo Wang, Zhongling YangAbstract:Multi-task concurrent execution and resource sharing based on preemptive scheduling strategy may cause Priority Inversion phenomenon in real-time systems. Priority Inversion phenomenon is the significant reason of unpredictable errors in real-time system; serious continuous Priority Inversion phenomenon will lead to real-time system collapse. The paper analyzes the phenomenon and the cause of the phenomenon, puts forward several design and implementation methods to solve Priority Inversion problem suitable for various application scenarios in μC/OS-II. A Priority exchange method is proposed to improve Priority inheritance protocol. The proposed method limit Priority Inversion phenomenon to one level. Theoretical analyses and experimental results indicate that the methods to solve the Priority Inversion problem in μC/OS-II are concise and effective, provides reasonable technical means for the safe running of complex real-time applications in μC/OS-II.
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research on subsystem hybrid scheduling and Priority Inversion based ucos ii
International Conference on Intelligent Networks and Intelligent Systems, 2012Co-Authors: Xibo WangAbstract:Uc/OS-II is an open-code real-time kernel based preemptive Priority scheduling strategy. It assigns a unique Priority for each task and does not support to schedule same Priority tasks. In practical applications, assigning different Priority for tasks which realizing the same function is not a very good logical design. Moreover it can only create a maximum of 64 tasks, which can not meet the needs of increasingly complex applications. Aiming at these problems, in the paper, the real time kernel uC/OS-II is modified. The new kernal creatively gives an approach of layered hybird scheduling for subsystem and jobs. The modified kernel divides a application system to some subsystems which is composed of several relevent jobs. There is a two layer hybird scheduling strategy which schedule subsystem based on Priority and schedule jobs in the subsystem based on Hybrid scheduling method. Preemptive scheduling based on Priority is adopted for jobs having different Priority in the subsystem, while, round-robin scheduling is adopted for jobs having the same Priority in the subsystem, which greatly augments application range of uC/OS-II. This paper also expounds the cause of Priority Inversion and the effect on system real-time performance, and two approaches named Priority inheritance protocol and Priority ceiling protocol are proposed to be used in uC/OS- ) for restraining Priority Inversion phenomenon. Eexperiments testing show that the proposed subsystem hybrid scheduling algorithm and the method to realize restraining Priority Inversion protocols in uC/OS-II are feasible and effective.
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Research on Subsystem Hybrid Scheduling and Priority Inversion Based uCOS-II
2012 Fifth International Conference on Intelligent Networks and Intelligent Systems, 2012Co-Authors: Xibo WangAbstract:Uc/OS-II is an open-code real-time kernel based preemptive Priority scheduling strategy. It assigns a unique Priority for each task and does not support to schedule same Priority tasks. In practical applications, assigning different Priority for tasks which realizing the same function is not a very good logical design. Moreover it can only create a maximum of 64 tasks, which can not meet the needs of increasingly complex applications. Aiming at these problems, in the paper, the real time kernel uC/OS-II is modified. The new kernal creatively gives an approach of layered hybird scheduling for subsystem and jobs. The modified kernel divides a application system to some subsystems which is composed of several relevent jobs. There is a two layer hybird scheduling strategy which schedule subsystem based on Priority and schedule jobs in the subsystem based on Hybrid scheduling method. Preemptive scheduling based on Priority is adopted for jobs having different Priority in the subsystem, while, round-robin scheduling is adopted for jobs having the same Priority in the subsystem, which greatly augments application range of uC/OS-II. This paper also expounds the cause of Priority Inversion and the effect on system real-time performance, and two approaches named Priority inheritance protocol and Priority ceiling protocol are proposed to be used in uC/OS-II for restraining Priority Inversion phenomenon. Experiments testing show that the proposed subsystem hybrid scheduling algorithm and the method to realize restraining Priority Inversion protocols in uC/OS-II are feasible and effective.
Don Towsley - One of the best experts on this subject based on the ideXlab platform.
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Priority inheritance in soft real-time databases
Real-Time Systems, 1992Co-Authors: Jiandong Huang, Krithi Ramamritham, John A. Stankovic, Don Towsley, Bhaskar PurimetlaAbstract:Due to resource sharing among tasks, Priority Inversion can occur during Priority-driven preemptive scheduling. In this work, we investigate solutions to the Priority Inversion problem in a soft real-time database environment where two-phhse locking is employed for concurrency control. We examine two basic schemes for addressing the Priority Inversion problem, one based on Priority inheritance and the other based on Priority abort. We also study a new scheme, called conditional Priority inheritance , which attempts to capitalize on the advantages of each of the two basic schemes. In contrast with previous results obtained in real-time operating systems, our performance studies, conducted on an actual real-time database testbed, indicate that the basic Priority inheritance protocol is inappropriate for solving the Priority Inversion problem in real-time database systems. We identify the reasons for this performance. We also show that the conditional Priority inheritance scheme and the Priority abort scheme perform well for a wide range of system workloads.
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RTSS - On using Priority inheritance in real-time databases
[1991] Proceedings Twelfth Real-Time Systems Symposium, 1991Co-Authors: Jiandong Huang, Krithi Ramamritham, John A. Stankovic, Don TowsleyAbstract:The authors investigate solutions to the Priority Inversion problem in a real-time database where two-phase locking is employed for concurrency control. They examine two basic schemes for addressing the Priority Inversion problem, one based on Priority inheritance and the other based on Priority abort. The authors also study a new scheme, called conditional Priority inheritance, which attempts to capitalize on the advantage of each of the two basic schemes. The performance studies, conducted on a real-time database testbed, indicated that the basic Priority inheritance protocol is inappropriate for solving the Priority Inversion problem in real-time database systems. The authors also show that the conditional Priority inheritance scheme and the Priority abort scheme perform well for a wide range of system workloads. >
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On using Priority inheritance in real-time databases
[1991] Proceedings Twelfth Real-Time Systems Symposium, 1991Co-Authors: Jiandong Huang, Krithi Ramamritham, John A. Stankovic, Don TowsleyAbstract:The authors investigate solutions to the Priority Inversion problem in a real-time database where two-phase locking is employed for concurrency control. They examine two basic schemes for addressing the Priority Inversion problem, one based on Priority inheritance and the other based on Priority abort. The authors also study a new scheme, called conditional Priority inheritance, which attempts to capitalize on the advantage of each of the two basic schemes. The performance studies, conducted on a real-time database testbed, indicated that the basic Priority inheritance protocol is inappropriate for solving the Priority Inversion problem in real-time database systems. The authors also show that the conditional Priority inheritance scheme and the Priority abort scheme perform well for a wide range of system workloads.