Systems that track sensed data trigger alerts based on the evaluation of some condition. In the p... more Systems that track sensed data trigger alerts based on the evaluation of some condition. In the presence of loss data a conservative condition may not generate a necessary alert and an aggressive condition may generate an alert that could have never happened. We observe that some lost values can be predicted and suggest new classes of conditions that provide more accurate alerts. We motivate the use of such conditions, provide a method for comparing two condition systems, and investigate the systems’ properties in both replicated and non replicated architectures. We prove two optimality results. In each one of them it is shown that a triggering algorithm, used in one of our condition systems, strictly dominates another algorithm for conservative system, yet, both algorithms satisfy the same set of properties. We show that a system can not be complete unless it is degenerate. Then we propose a weak completeness property, discuss its merit and show a motivation for its use.
ABSTRACT Workflow systems utilize a process model for managing business processes. The model is t... more ABSTRACT Workflow systems utilize a process model for managing business processes. The model is typically a directed graph annotated with activity names. We view the execution of an activity as a time interval, and present two new algorithms for synthesizing process models from sets of systems' executions (audit log). A model graph generated by each of the algorithms for a process captures all its executions and dependencies that are present in the log, and preserves existing parallelism. We compare the model graphs synthesized by our algorithms to those of [1] by running themon simulated data. We observe that our graphs are more faithful in the sense that the number of excess and missing edges is consistently smaller and it depends on the size and quality of the log. In other words, we show that our time interval approach permits reconstruction of more accurate workflow model graphs from a log.
Fig. 1 is an example of a workflow model graph and two legal flow subgraphs. In flow (a), the con... more Fig. 1 is an example of a workflow model graph and two legal flow subgraphs. In flow (a), the control function is evaluated to 0 on the edge from A to C and on the edge from B to D. In flow (b), the value is 0 on the edge from B to C. Execution (A, B, C, D) is a legal execution in both flows, but (A, C, B, D) is a legal execution only in flow (b). Those are also the only legal executions in our example.
We introduce a scheduling model, inspired by data flow computers, in which the overhead incurred ... more We introduce a scheduling model, inspired by data flow computers, in which the overhead incurred in a system as well as computation time are described explicitly. Using this model, we provide algorithms for partitioning programs so as to minimize their completion time. In the traditional data flow paradigm, every instruction is considered a "task", and it is scheduled for execution as early as possible. Implementations of this scheme, however, involve overheads which affect the running time of the programs. We propose to partition the program into larger grains, each containing one or more instructions, such that scheduling those grains would result in minimizing the completion time. Our model accounts for both the overhead incurred when executing a program and the actual execution time of its instructions. Within this framework we derive lower and upper bounds on the execution time of programs represented as trees and DAGs. We provide algorithms for optimally partitioning...
Proceedings of the International Conference on Mobile Ad-hoc and Sensor Networks (MSN), Wuhan, China, Lecture Notes in Computer Science, Dec 2005
Abstract. Systems that track sensed data trigger alerts based on the evaluation of some condition... more Abstract. Systems that track sensed data trigger alerts based on the evaluation of some condition. In the presence of loss data a conservative condition may not generate a necessary alert and an aggressive condition may generate an alert that could have never happened. We observe that some lost values can be predicted and suggest new classes of conditions that provide more accurate alerts. We motivate the use of such conditions, provide a method for comparing two condition systems, and investigate the systems ’ properties in both replicated and non replicated architectures. In addition, we propose a weak completeness property, discuss its merit and show a motivation for its use. Our main result shows that a triggering algorithm, used in one of our condition systems, strictly dominates another algorithm for conservative system, yet, both algorithms satisfy the same set of properties; thus, with some simple observations, we have a strong evidence for its optimality. 1
Abstract. This paper considers a variant of the Byzantine Generals problem, in which processes st... more Abstract. This paper considers a variant of the Byzantine Generals problem, in which processes start with arbitrary real values rather than Boolean values or values from some bounded range, and in which approximate, rather than exact, agreement is the desired goal. Algorithms are presented to reach approximate agreement in asynchronous, as well as synchronous systems. The asynchronous agreement algorithm is an interesting contrast to a result of Fischer et al, who show that exact agreement with guaranteed termination is not attainable in an asynchronous system with as few as one faulty process. The algorithms work by successive approximation, with a provable convergence rate that depends on the ratio between the number of faulty processes and the total number of processes. Lower bounds on the convergence rate for algorithms of this form are proved, and the algorithms presented are shown to
... A simpler version of the node organization algorithm provides a distributed coloring algorith... more ... A simpler version of the node organization algorithm provides a distributed coloring algorithm, which is highly localized, robust, and can operate on a dynamic graph in the face ... is bounded by K + 1 and the bound is reached only when there are at least K(K + 1)/2 edges in the ...
International Journal of High Performance Computing and Networking, 2008
ABSTRACT Machine virtualisation is a key technology for server consolidation and on-demand server... more ABSTRACT Machine virtualisation is a key technology for server consolidation and on-demand server provisioning. To support this trend, it is essential to improve the performance of virtualisation software and enable the efficient running of many virtual machines. We present a virtualisation system that can dynamically extend the real memory of its guest virtual machines. We describe an implementation of dynamic memory extension for Linux guests running on the IBM zVM virtualisation environment. Our implementation utilises device drivers for accessing dynamic memory extensions. We show that this capability can improve utilisation and performance of the Linux guests in our virtualisation environment.
Systems that track sensed data trigger alerts based on the evaluation of some condition. In the p... more Systems that track sensed data trigger alerts based on the evaluation of some condition. In the presence of loss data a conservative condition may not generate a necessary alert and an aggressive condition may generate an alert that could have never happened. We observe that some lost values can be predicted and suggest new classes of conditions that provide more accurate alerts. We motivate the use of such conditions, provide a method for comparing two condition systems, and investigate the systems’ properties in both replicated and non replicated architectures. We prove two optimality results. In each one of them it is shown that a triggering algorithm, used in one of our condition systems, strictly dominates another algorithm for conservative system, yet, both algorithms satisfy the same set of properties. We show that a system can not be complete unless it is degenerate. Then we propose a weak completeness property, discuss its merit and show a motivation for its use.
ABSTRACT Workflow systems utilize a process model for managing business processes. The model is t... more ABSTRACT Workflow systems utilize a process model for managing business processes. The model is typically a directed graph annotated with activity names. We view the execution of an activity as a time interval, and present two new algorithms for synthesizing process models from sets of systems' executions (audit log). A model graph generated by each of the algorithms for a process captures all its executions and dependencies that are present in the log, and preserves existing parallelism. We compare the model graphs synthesized by our algorithms to those of [1] by running themon simulated data. We observe that our graphs are more faithful in the sense that the number of excess and missing edges is consistently smaller and it depends on the size and quality of the log. In other words, we show that our time interval approach permits reconstruction of more accurate workflow model graphs from a log.
Fig. 1 is an example of a workflow model graph and two legal flow subgraphs. In flow (a), the con... more Fig. 1 is an example of a workflow model graph and two legal flow subgraphs. In flow (a), the control function is evaluated to 0 on the edge from A to C and on the edge from B to D. In flow (b), the value is 0 on the edge from B to C. Execution (A, B, C, D) is a legal execution in both flows, but (A, C, B, D) is a legal execution only in flow (b). Those are also the only legal executions in our example.
We introduce a scheduling model, inspired by data flow computers, in which the overhead incurred ... more We introduce a scheduling model, inspired by data flow computers, in which the overhead incurred in a system as well as computation time are described explicitly. Using this model, we provide algorithms for partitioning programs so as to minimize their completion time. In the traditional data flow paradigm, every instruction is considered a "task", and it is scheduled for execution as early as possible. Implementations of this scheme, however, involve overheads which affect the running time of the programs. We propose to partition the program into larger grains, each containing one or more instructions, such that scheduling those grains would result in minimizing the completion time. Our model accounts for both the overhead incurred when executing a program and the actual execution time of its instructions. Within this framework we derive lower and upper bounds on the execution time of programs represented as trees and DAGs. We provide algorithms for optimally partitioning...
Proceedings of the International Conference on Mobile Ad-hoc and Sensor Networks (MSN), Wuhan, China, Lecture Notes in Computer Science, Dec 2005
Abstract. Systems that track sensed data trigger alerts based on the evaluation of some condition... more Abstract. Systems that track sensed data trigger alerts based on the evaluation of some condition. In the presence of loss data a conservative condition may not generate a necessary alert and an aggressive condition may generate an alert that could have never happened. We observe that some lost values can be predicted and suggest new classes of conditions that provide more accurate alerts. We motivate the use of such conditions, provide a method for comparing two condition systems, and investigate the systems ’ properties in both replicated and non replicated architectures. In addition, we propose a weak completeness property, discuss its merit and show a motivation for its use. Our main result shows that a triggering algorithm, used in one of our condition systems, strictly dominates another algorithm for conservative system, yet, both algorithms satisfy the same set of properties; thus, with some simple observations, we have a strong evidence for its optimality. 1
Abstract. This paper considers a variant of the Byzantine Generals problem, in which processes st... more Abstract. This paper considers a variant of the Byzantine Generals problem, in which processes start with arbitrary real values rather than Boolean values or values from some bounded range, and in which approximate, rather than exact, agreement is the desired goal. Algorithms are presented to reach approximate agreement in asynchronous, as well as synchronous systems. The asynchronous agreement algorithm is an interesting contrast to a result of Fischer et al, who show that exact agreement with guaranteed termination is not attainable in an asynchronous system with as few as one faulty process. The algorithms work by successive approximation, with a provable convergence rate that depends on the ratio between the number of faulty processes and the total number of processes. Lower bounds on the convergence rate for algorithms of this form are proved, and the algorithms presented are shown to
... A simpler version of the node organization algorithm provides a distributed coloring algorith... more ... A simpler version of the node organization algorithm provides a distributed coloring algorithm, which is highly localized, robust, and can operate on a dynamic graph in the face ... is bounded by K + 1 and the bound is reached only when there are at least K(K + 1)/2 edges in the ...
International Journal of High Performance Computing and Networking, 2008
ABSTRACT Machine virtualisation is a key technology for server consolidation and on-demand server... more ABSTRACT Machine virtualisation is a key technology for server consolidation and on-demand server provisioning. To support this trend, it is essential to improve the performance of virtualisation software and enable the efficient running of many virtual machines. We present a virtualisation system that can dynamically extend the real memory of its guest virtual machines. We describe an implementation of dynamic memory extension for Linux guests running on the IBM zVM virtualisation environment. Our implementation utilises device drivers for accessing dynamic memory extensions. We show that this capability can improve utilisation and performance of the Linux guests in our virtualisation environment.
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Papers by Shlomit S Pinter