29393244
Semantic Caching and Query Processing
Semantic caching is very attractive for use in distributed systems due to the reduced network traffic and the improved response time. It is particularly efficient for a mobile computing environment, where the bandwidth of wireless links is a major performance bottleneck. Previous work either does not provide a formal semantic caching model, or lacks efficient query processing strategies. This paper extends the existing research in three ways: formal definitions associated with semantic caching are presented, query processing strategies are investigated and, finally, the performance of the semantic cache model is examined through a detailed simulation study.
39362526
Main memory database recovery algorithms and their performance
In main memory systems recovery becomes more complex mainly due to the volatility of main memory and the elimination of the separation of data storage (disk) and data processing locations (main memory). In a disk based database system, it is the disk copy that represents the stable database restored after a system failure; but in MDBSs, the main memory copy of the database must be recovered. The paper discusses the recovery issues in MDBSs and presents a somewhat detailed performance study of two recovery algorithms, one using a shadow approach and the other update-in-place.<<ETX>>
34436430
An Integrated Data Structure with Multiple Access Paths for Database Systems and its Performance
Abstract In the past a number of file organizations have been proposed for processing different types of queries efficiently. To our knowledge none of the existing file organizations is capable of supporting all types of accesses equally efficiently. In this paper we have taken a different approach for designing an integated data structure which offers multiple access paths for processing different types of queries efficiently. The data structure reported here can be implemented on disk based as well as main memory database systems, however, in this paper we report its behavior mainly in main memory database environment. Our approach is to fuse those data structures which offer an efficient access paths for a particular type. To show the feasibility of our scheme we fused the B+-tree, the grid file and extendible hashing structures, using a proper interface. We implemented and measured its performance through simulation modeling. Our results show that the data structure does improve concurrency and offers a higher throughput for a variety of transaction processing workloads. We argue that our scheme is different than creating secondary indexes for improving concurrency. In the absence of a data strucure which can provide all types of access equally efficiently, an integrated data structure is an acceptable solution which offers an efficient way for increasing the performance of database management systems.
18803353
Performance of Multiversion and Distributed Two-Phase Locking Concurrency Control Mechanisms in Distributed Databases
In this paper, we have presented a detailed simulation study of a distributed multiversion and a distributed two-phase locking concurrency control mechanism (CCM). Our experiment concentrated on measuring the effect of message overhead, read:write ratios, data partitioning, and partial replication on the performance of these mechanisms. The effect of these parameters has not been investigated in any previous work. We simultated a blind-write model for two reasons: (a) all other works studied the behavior of multiversion CCMs under read-before-write model and observed a similar result, and (b) the performance of any multiversion CCM has not been studied under a blind-write model. A blind-write model is not unrealistic, and intutively the multiversion should provide much better performance. We observed that multiversion outperforms wound-wait (WW) in both partitioned and partially replicated databases. Multi version (MV) handles read-only and write-only transactions efficiently, and after a certain write percentage the throughput improves with this percentage. The message overhead progressively becomes less significant as the MPL (multiprogramming level) increases, indicating that in a heavily loaded system the throughput is least sensitive to message cost. We found that in the partially replicated case, 50% write does not show the lowest performance, as observed in the partitioned case.
42935672
Performance Measurement of Main Memory Database Recovery Algorithms Based on Update-in-Place and Shadow Approaches
The authors present a performance study of two main memory database recovery algorithms, one using a shadow approach and the other update-in-place. The results show that in main memory databases, shadow approach performs better than update-in-place. The authors introduce minor improvements to the shadow scheme and show that the modified algorithm does show further performance improvement. >
35078097
An adaptive location management algorithm for mobile computing
In mobile computing mobile hosts or mobile units move randomly from one place to another within a well-defined geographical area. This requires some mechanism for identifying the exact location of a mobile host. Such mechanisms are usually referred to as location management and is one of the essential components for supporting mobility. In the past a number of efficient location management schemes have been suggested but they lack adaptability. We believe that an adaptable location management scheme is more desirable because of frequent change in the location of mobile hosts. In this paper, we report a location management algorithm, which adapts to the constant changing scenario. Our algorithm makes use of some of the concepts of location management schemes proposed in the past.
5164784
Hierarchical modeling and analysis of embedded systems
This paper describes the modeling language CHARON for modular design of interacting hybrid systems. The language allows specification of architectural as well as behavioral hierarchy and discrete as well as continuous activities. The modular structure of the language is not merely syntactic, but is exploited by analysis tools and is supported by a formal semantics with an accompanying compositional theory of refinement. We illustrate the benefits of CHARON in the design of embedded control software using examples from automated highways concerning vehicle coordination.
10015251
Repartitioning of Adaptive Meshes: Experiments with Multilevel Diffusion
For a large class of irregular grid applications, the structure of the mesh changes from one phase of the computation to the next. Eventually, as the graph evolves, the adapted mesh has to be repartitioned to ensure good load balance. If this new graph is partitioned from scratch, it will lead to an excessive migration of data among processors. In this paper, we present a new scheme for computing repartitionings of adaptively refined meshes. This scheme performs diffusion of vertices in a multilevel framework and minimizes vertex movement without significantly compromising the edge-cut.
5797236
Strong edge coloring for channel assignment in wireless radio networks
We give efficient sequential and distributed approximation algorithms for strong edge coloring graphs modeling wireless networks. Strong edge coloring is equivalent to computing a conflict-free assignment of channels or frequencies to pairwise links between transceivers in the network
30844152
Multiple cooperating mobile manipulators
The main goal of the paper is to present a framework and basic control algorithms for coordinating a small team of robots in tasks that involve grasping large objects and transporting them in a two-dimensional environment with obstacles. Each robot consists of a mobile platform and an arm. Some arms are passive while others are active. Our previous work (1998) addressed the manipulator design, the architecture, and the communication between robots. In this paper we address the control of the manipulators, the coordination between the platforms for a team of two or three cooperating robots, and the handling of flexible large objects.
18650185
Minimization, Learning, and Conformance Testing of Boolean Programs
Boolean programs with recursion are convenient abstractions of sequential imperative programs, and can be represented as recursive state machines (RSMs) or pushdown automata. Motivated by the special structure of RSMs, we define a notion of modular visibly pushdown automata (modular VPA) and show that for the class of languages accepted by such automata, unique minimal modular VPA exist. This yields an efficient approximate minimization theorem that minimizes RSMs to within a factor of k of the minimal RSM, where k is the maximum number of parameters in any module. Using the congruence defined for minimization, we show an active learning algorithm (with a minimally adequate teacher) for context free languages in terms of modular VPAs. We also present an algorithm that constructs complete test suites for Boolean program specifications. Finally, we apply our results on learning and test generation to perform model checking of black-box Boolean programs.