26676459
Progressive Transaction Recovery in Distributed DB/DC Systems
The demand for on-line transaction processing has grown rapidly in recent years. To meet the transaction demand, several DB (database management) and DC (data communication management) subsystems can be coupled together to form a distributed DB/DC system. A key problem is to provide these distributed systems with effective means to recover transactions upon failure while paying little performance penalty during normal processing. Also, there should be minimal interference of fault-free components, during the recovery of failed component. By decentralizing recovery management, and using transaction level structural information to eliminate costly lower level handshaking protocols, proposed progressive transaction recovery protocols seek to solve the problem. A queueing model for evaluating the transaction response time during normal processing for the progressive and pessimistic protocols is developed and solved, via simulation. The progressive recovery protocols are shown to reduce normal processing overhead and lead to performance improvement over the pessimistic protocol.
40618061
Transaction Recovery in Distributed DB/DC Systems: A Progressive Approach
31591898
Scanning the issue - special issue on real-time systems
920212
Resource scheduling in dependable integrated modular avionics
In the recent development of avionics systems, integrated modular avionics (IMA) is advocated for next generation architecture that needs integration of mixed criticality real-time applications. These integrated applications meet their own timing constraints while sharing avionics computer resources. To guarantee timing constraints and dependability of each application, an IMA-based system is equipped with the schemes for spatial and temporal partitioning. We refer the model as SP-RTS (strongly partitioned real-time system), which deals with processor partitions and communication channels as its basic scheduling entities. This paper presents a partition and channel-scheduling algorithm for the SP-RTS. The basic idea of the algorithm is to use a two-level hierarchical schedule that activates partitions (or channels) following a distance-constraints guaranteed cyclic schedule and then dispatches tasks (or messages) according to a fixed priority schedule. To enhance schedulability, we devised heuristic algorithms for deadline decomposition and channel combining. The simulation results show the schedulability analysis of the two-level scheduling algorithm and the beneficial characteristics of the proposed deadline decomposition and channel combining algorithms.
10753893
Evaluation of Error Recovery Blocks Used for Cooperating Processes
Three alternatives for implementing recovery blocks (RB's) are conceivable for backward error recovery in concurrent processing. These are the asynchronous, synchronous, and the pseudorecovery point implementations. Asynchronous RB's are based on the concept of maximum autonomy in each of concurrent processes. Consequently, establishment of RB's in a process is made independently of others and unbounded rollback propagations become a serious problem. In order to completely avoid unbounded rollback propagations, it is necessary to synchronize the establishment of recovery blocks in all cooperating processes. Process autonomy is sacrificed and processes are forced to wait for commitments from others to establish a recovery line, leading to inefficiency in time utilization. As a compromise between asynchronous and synchronous RB's we propose to insert pseudorecovery points (PRP's) so that unbounded rollback propagations may be avoided while maintaining process autonomy. We developed probabilistic models for analyzing these three methods under standard assumptions in computer performance analysis, i.e., exponential distributions for related random variables. With these models we have estimated 1) the interval between two successive recovery lines for asynchronous RB's, 2) mean loss in computation power for the synchronized method, and 3) additional overhead and rollback distance in case PRP's are used.
206579905
Improving multistage network performance under uniform and hot-spot traffics
The major performance drawbacks of multistage interconnection networks are due to link contention and message blockage. To remedy this problem, the authors propose a switch design which uses two independent routes between each input port and each output port within a switch. With proper routing control mechanisms, the adverse effect on link conflicts can be greatly reduced. Various simulations are used to illustrate the performance improvement of this new design under both uniform and hot-spot traffic patterns.<<ETX>>
7927244
GM-WTA: An efficient workflow task allocation method in a distributed execution environment
A workflow is a collection of units of work called workflow tasks which cooperatively realize a business objective by utilizing system resources such as databases. The roles of workflow tasks are performed in the order driven by a computer representation of the workflow logic. During completing each task's role, the remote control transfers and the remote resource accesses may often occur in a distributed workflow system. Hence, the efficient distribution of workflow components, especially workflow tasks, is so effective as to improve the performance of workflow processing. If we can place adjacent workflow tasks as close as possible and locate workflow tasks near to the required resources, we can significantly reduce the overhead of workflow processing.In this paper, we propose an efficient workflow task allocation method in a distributed workflow system, which is based on the locality principle. The method that utilizes the concept of graph partitioning can improve the performanace of workflow processing by minimizing the remote processing costs incurred during workflow execution. In addition, we perform several experiments to evaluate our proposed method.
2382569
Filtering XPath expressions for XML access control
XPath is a standard for specifying parts of XML documents and a suitable language for both query processing and access control of XML. In this paper, we use the XPath expression for representing user queries and access control for XML. And we propose an access-control method for XML, where we control accesses to XML documents by filtering query XPath expressions through access-control XPath expressions. For filtering the access-denied parts out of query XPath expressions, set operations (such as, intersection and difference) between the XPath expressions are essential. However, it is known that the containment problem of two XPath expressions is coNP-hard when the XPath expressions contain predicates (or branch), wildcards and descendant axes. To solve the problem, we directly search XACT (XML Access Control Tree) for a query XPath expression and extract the access-granted parts. The XACT is our proposed structure, where the edges are structural summary of XML elements and the nodes contain access-control information. We show that the query XPath expressions are successfully filtered through the XACT by our proposed method, and also show the performance improvement by comparing the proposed method with the previous work.
5961676
Total Data Quality Management: The Case of IRI
Abstract Implementing a Total Data Quality Management (TDQM) program is not a trivial undertaking. Two key steps are (1) to clearly define what an organization means by data quality and (2) to develop metrics that measure data quality dimensions and that are linked to the organization’s goals and objectives. This paper presents the case of Information Resources, Inc., which exemplifies how a company can develop a viable TDQM program.
9854601
An effective recovery under fuzzy checkpointing in main memory databases
Abstract In main memory databases, fuzzy checkpointing gives less transaction overhead due to its asynchronous backup feature. However, till now, fuzzy checkpointing has considered only physical logging schemes. The size of the physical log records is very large, and hence it incurs space and recovery processing overhead. In this paper, we propose a recovery method based on a hybrid logging scheme, which permits logical logging under fuzzy checkpointing. The proposed method significantly reduces the size of log data, and hence offers faster recovery processing than other conventional fuzzy checkpointing with physical logging.
404374
The Learning and Emergence of Mildly Context Sensitive Languages
This paper describes a framework for studies of the adaptive acquisition and evolution of language, with the following components: language learning begins by associating words with cognitively salient representations (“grounding”); the sentences of each language are determined by properties of lexical items, and so only these need to be transmitted by learning; the learnable languages allow multiple agreements, multiple crossing agreements, and reduplication, as mildly context sensitive and human languages do; infinitely many different languages are learnable; many of the learnable languages include infinitely many sentences; in each language, inferential processes can be defined over succinct representations of the derivations themselves; the languages can be extended by innovative responses to communicative demands. Preliminary analytic results and a robotic implementation are described.