Bounded disorder file organization

The bounded disorder file organization proposed by W. Litwin and D.B. Lomet (1987) uses a combination of hashing and tree indexing. Lomet provided an approximate analysis with the mention of the difficulty involved in exact modeling of data nodes, which motivated this work. In an earlier paper (M.V. Ramakrishna and P. Mukhopadhyay, 1988) we provided an exact model and analysis of the data nodes, which is based on the solution of a classical sequential occupancy problem. After summarizing the analysis of data nodes, an alternate file growth method based on repeated trials using universal hashing is proposed and analyzed. We conclude that the alternate file growth method provides simplicity and significant improvement in storage utilization     

Reaching approximate agreement with mixed-mode faults

In a fault-tolerant distributed system, different non-faulty processes may arrive at different values for a given system parameter. To resolve this disagreement, processes must exchange and vote upon their respective local values. Faulty processes may attempt to inhibit agreement by acting in a malicious or “Byzantine” manner. Approximate agreement defines one form of agreement in which the voted values obtained by the non-faulty processes need not be identical. Instead, they need only agree to within a predefined tolerance. Approximate agreement can be achieved by a sequence of convergent voting rounds, in which the range of values held by non-faulty processes is reduced in each round. Historically, each new convergent voting algorithm has been accompanied by ad-hoc proofs of its convergence rate and fault-tolerance, using an overly conservative fault model in which all faults exhibit worst-case Byzantine behavior. This paper presents a general method to quickly determine convergence rate and fault-tolerance for any member of a broad family of convergent voting algorithms. This method is developed under a realistic mixed-mode fault model comprised of asymmetric, symmetric, and benign fault modes. These results are employed to more accurately analyze the properties of several existing voting algorithms, to derive a sub-family of optimal mixed-mode voting algorithms, and to quickly determine the properties of proposed new voting algorithms     

Machine independent AND and OR parallel execution of logicprograms. I. The binding environment

We describe a binding environment for the AND and OR parallel execution of logic programs that is suitable for both shared and nonshared memory multiprocessors. The binding environment was designed with a view of rendering a compiler using this binding environment machine independent. The binding environment is similar to closed environments proposed by J. Conery. However, unlike Conery's scheme, it supports OR and independent AND parallelism on both types of machines. The term representation, the algorithms for unification and the join algorithms for parallel AND branches are presented in this paper. We also detail the differences between our scheme and Conery's scheme. A compiler based on this binding environment has been implemented on a platform for machine independent parallel programming called the Chare Kernel     

On loop transformations for generalized cycle shrinking

This paper describes several loop transformation techniques for extracting parallelism from nested loop structures. Nested loops can then be scheduled to run in parallel so that execution time is minimized. One technique is called selective cycle shrinking, and the other is called true dependence cycle shrinking. It is shown how selective shrinking is related to linear scheduling of nested loops and how true dependence shrinking is related to conflict-free mappings of higher dimensional algorithms into lower dimensional processor arrays. Methods are proposed in this paper to find the selective and true dependence shrinkings with minimum total execution time by applying the techniques of finding optimal linear schedules and optimal and conflict-free mappings proposed by W. Shang and A.B. Fortes     

Structuring fault-tolerant object systems for modularity in adistributed environment

The object-oriented approach to system structuring has found widespread acceptance among designers and developers of robust computing systems. The authors propose a system structure for distributed programming systems that support persistent objects and describe how properties such as persistence and recoverability can be implemented. The proposed structure is modular, permitting easy exploitation of any distributed computing facilities provided by the underlying system. An existing system constructed according to the principles espoused here is examined to illustrate the practical utility of the proposed approach to system structuring     

Scheduling DAG's for asynchronous multiprocessor execution

A new approach is given for scheduling a sequential instruction stream for execution “in parallel” on asynchronous multiprocessors. The key idea in our approach is to exploit the fine grained parallelism present in the instruction stream. In this context, schedules are constructed by a careful balancing of execution and communication costs at the level of individual instructions, and their data dependencies. Three methods are used to evaluate our approach. First, several existing methods are extended to the fine grained situation. Our approach is then compared to these methods using both static schedule length analyses, and simulated executions of the scheduled code. In each instance, our method is found to provide significantly shorter schedules. Second, by varying parameters such as the speed of the instruction set, and the speed/parallelism in the interconnection structure, simulation techniques are used to examine the effects of various architectural considerations on the executions of the schedules. These results show that our approach provides significant speedups in a wide-range of situations. Third, schedules produced by our approach are executed on a two-processor Data General shared memory multiprocessor system. These experiments show that there is a strong correlation between our simulation results, and these actual executions, and thereby serve to validate the simulation studies. Together, our results establish that fine grained parallelism can be exploited in a substantial manner when scheduling a sequential instruction stream for execution “in parallel” on asynchronous multiprocessors     

On the performance of synchronized programs in distributed networkswith random processing times and transmission delays

A synchronizer is a compiler that transforms a program designed to run in a synchronous network into a program that runs in an asynchronous network. The behavior of a simple synchronizer, which also represents a basic mechanism for distributed computing and for the analysis of marked graphs, was studied by S. Even and S. Rajsbaum (1990) under the assumption that message transmission delays and processing times are constant. We study the behavior of the simple synchronizer when processing times and transmission delays are random. The main performance measure is the rate of a network, i.e., the average number of computational steps executed by a processor in the network per unit time. We analyze the effect of the topology and the probability distributions of the random variables on the behavior of the network. For random variables with exponential distribution, we provide tight (i.e., attainable) bounds and study the effect of a bottleneck processor on the rate     

On the design of dynamic associative neural memories

We consider the design problem for a class of discrete-time and continuous-time neural networks. We obtain a characterization of all connection weights that store a given set of vectors into the network, that is, each given vector becomes an equilibrium point of the network. We also give sufficient conditions that guarantee the asymptotic stability of these equilibrium points.