基于客户端缓存提高Java RMI性能的方法

Java中的远程方法调用是实现分布式系统的主要技术之一,但在实际应用中,过多重复的远程方法调用会影响程序性能.给出了一种基于客户端缓存的RMI方法,使用客户端本地缓存保存使用过的存根和结果,当客户端需要调用远程方法时首先查询缓存中是否存在将要调用的存根或结果,如果存在就直接从缓存中返回而不需要通过网络进行RMI调用.经过性能比较可以发现客户端缓存的加入能有效减少重复RMI调用的次数,从而提高程序响应速度并减少了占用的网络带宽.     

Proxy cache algorithms: design, implementation, and performance

Caching at proxy servers is one of the ways to reduce the response time perceived by World Wide Web users. Cache replacement algorithms play a central role in the response time reduction by selecting a subset of documents for caching, so that a given performance metric is maximized. At the same time, the cache must take extra steps to guarantee some form of consistency of the cached documents. Cache consistency algorithms enforce appropriate guarantees about the staleness of the cached documents. We describe a unified cache maintenance algorithm, LNC-R-WS-U, which integrates both cache replacement and consistency algorithms. The LNC-R-WS-U algorithm evicts documents from the cache based on the delay to fetch each document into the cache. Consequently, the documents that took a long time to fetch are preferentially kept in the cache. The LNC-R-W3-U algorithm also considers in the eviction consideration the validation rate of each document, as provided by the cache consistency component of LNC-R-WS-U. Consequently, documents that are infrequently updated and thus seldom require validations are preferentially retained in the cache. We describe the implementation of LNC-R-W3-U and its integration with the Apache 1.2.6 code base. Finally, we present a trace-driven experimental study of LNC-R-W3-U performance and its comparison with other previously published algorithms for cache maintenance     

Massively parallel algorithms for trace-driven cache simulations

Considers the use of massively parallel architectures to execute a trace-driven simulation of a single cache set. A method is presented for the least-recently-used (LRU) policy, which, regardless of the set size C, runs in time O(log N) using N processors on the EREW (exclusive read, exclusive write) parallel model. A simpler LRU simulation algorithm is given that runs in O(C log N) time using N/log N processors. We present timings of this algorithm's implementation on the MasPar MP-1, a machine with 16384 processors. A broad class of reference-based line replacement policies are considered, which includes LRU as well as the least-frequently-used (LFU) and random replacement policies. A simulation method is presented for any such policy that, on any trace of length N directed to a C line set, runs in O(C log N) time with high probability using N processors on the EREW model. The algorithms are simple, have very little space overhead, and are well suited for SIMD implementation     

Orderly algorithms for graph generation

The existence of orderly analogues of graph generators proposed by Heap and Farrell is established. The modifications to these algorithms supply practical methods enabling one to generate exhaustive lists of graphs and locally restricted graphs; moreover, the difficulty involved in ensuring that no duplications occur in the list is greatly reduced.     

Scalable cache invalidation algorithms for mobile data access

In this paper, we address the problem of cache invalidation in mobile and wireless client/server environments. We present cache invalidation techniques that can scale not only to a large number of mobile clients, but also to a large number of data items that can be cached in the mobile clients. We propose two scalable algorithms: the Multidimensional Bit-Sequence (MD-BS) algorithm and the Multilevel Bit-Sequence (ML-BS) algorithm. Both algorithms are based on our prior work on the Basic Bit-Sequences (BS) algorithm. Our study shows that the proposed algorithms are effective for a large number of cached data items with low update rates. The study also illustrates that the algorithms ran be used with other complementary techniques to address the problem of cache invalidation for data items with varied update and access rates.     

Efficient parallel algorithms for graph problems

We present an efficient technique for parallel manipulation of data structures that avoids memory access conflicts. That is, this technique works on the Exclusive Read/Exclusive Write (EREW) model of computation, which is the weakest shared memory, MIMD machine model. It is used in a new parallel radix sort algorithm that is optimal for keys whose values are over a small range. Using the radix sort and known results for parallel prefix on linked lists, we develop parallel algorithms that efficiently solve various computations on trees and “unicycular graphs.” Finally, we develop parallel algorithms for connected components, spanning trees, minimum spanning trees, and other graph problems. All of the graph algorithms achieve linear speedup for all but the sparsest graphs.     

Efficient parallel algorithms for graph problems

We present an efficient technique for parallel manipulation of data structures that avoids memory access conflicts. That is, this technique works on the Exclusive Read/Exclusive Write (EREW) model of computation, which is the weakest shared memory, MIMD machine model. It is used in a new parallel radix sort algorithm that is optimal for keys whose values are over a small range. Using the radix sort and known results for parallel prefix on linked lists, we develop parallel algorithms that efficiently solve various computations on trees and unicycular graphs. Finally, we develop parallel algorithms for connected components, spanning trees, minimum spanning trees, and other graph problems. All of the graph algorithms achieve linear speedup for all but the sparsest graphs.Part of this work was done while the first author was at the University of Illinois, Urbana-Champaign, the second author was at Carnegie-Mellon University, and the third author was at the Hebrew University and the Courant Institute of Mathematical Sciences, New York University. A preliminary version of this work was presented at the 1986 International Conference on Parallel Processing.     

Priority algorithms for graph optimization problems

We continue the study of priority or “greedy-like” algorithms as initiated in Borodin et al. (2003) [10] and as extended to graph theoretic problems in Davis and Impagliazzo (2009) [12]. Graph theoretic problems pose some modeling problems that did not exist in the original applications of Borodin et al. and Angelopoulos and Borodin (2002) [3]. Following the work of Davis and Impagliazzo, we further clarify these concepts. In the graph theoretic setting, there are several natural input formulations for a given problem and we show that priority algorithm bounds in general depend on the input formulation. We study a variety of graph problems in the context of arbitrary and restricted priority models corresponding to known “greedy algorithms”.     

Optimizing CAM-based instruction cache designs for low-power embedded systems

Energy consumption and power dissipation are important concerns in the design of embedded systems and they will become even more crucial with finer process geometry, higher frequencies, deeper pipelines and wider issue designs. In particular, the instruction cache consumes more energy than any other processor module, especially with commonly used highly associative CAM-based implementations.Two energy-efficient approaches for highly associative CAM-based instruction cache designs are presented by means of using a segmented wordline and a predictor-based instruction fetch mechanism. The latter is based on the fact that not all instructions in a given I-cache fetch are used due to taken branches. The proposed Fetch Mask Predictor unit determines which instructions in a cache access will actually be used to avoid fetching any of the other instructions. Both proposed approaches are evaluated for an embedded 4-wide issue processor in 100 nm technology. Experimental results show average I-cache energy savings of 48% and overall processor energy savings of 19%.     

Combinatorial algorithms for distributed graph coloring

Numerous problems in Theoretical Computer Science can be solved very efficiently using powerful algebraic constructions. Computing shortest paths, constructing expanders, and proving the PCP Theorem, are just few examples of this phenomenon. The quest for combinatorial algorithms that do not use heavy algebraic machinery, but are roughly as efficient, has become a central field of study in this area. Combinatorial algorithms are often simpler than their algebraic counterparts. Moreover, in many cases, combinatorial algorithms and proofs provide additional understanding of studied problems. In this paper we initiate the study of combinatorial algorithms for Distributed Graph Coloring problems. In a distributed setting a communication network is modeled by a graph $G=(V,E)$ of maximum degree $\varDelta $ . The vertices of $G$ host the processors, and communication is performed over the edges of $G$ . The goal of distributed vertex coloring is to color $V$ with $(\varDelta + 1)$ colors such that any two neighbors are colored with distinct colors. Currently, efficient algorithms for vertex coloring that require $O(\varDelta + \log ^* n)$ time are based on the algebraic algorithm of Linial (SIAM J Comput 21(1):193–201, 1992) that employs set-systems. The best currently-known combinatorial set-system free algorithm, due to Goldberg et al. (SIAM J Discret Math 1(4):434–446, 1988), requires $O(\varDelta ^2+\log ^*n)$ time. We significantly improve over this by devising a combinatorial $(\varDelta + 1)$ -coloring algorithm that runs in $O(\varDelta + \log ^* n)$ time. This exactly matches the running time of the best-known algebraic algorithm. In addition, we devise a tradeoff for computing $O(\varDelta \cdot t)$ -coloring in $O(\varDelta /t + \log ^* n)$ time, for almost the entire range $1 < t < \varDelta $ . We also compute a Maximal Independent Set in $O(\varDelta + \log ^* n)$ time on general graphs, and in $O(\log n/ \log \log n)$ time on graphs of bounded arboricity. Prior to our work, these results could be only achieved using algebraic techniques. We believe that our algorithms are more suitable for real-life networks with limited resources, such as sensor networks.     

Two graph algorithms derived

Much emphasis has been placed in recent years on deriving or calculating programs rather than proving them correct. Adequate calculational frameworks are needed to support such an approach. The present work explores the use of a calculus of relations to express and reason about graph properties in an algorithmic context. We first construct a generic program that computes a maximal set, over some universe, satisfying a certain given predicate. The development is presented as a step-by-step derivation, applying well-known techniques and heuristics that aid the construction of imperative programs. A calculational framework of relations is then used to obtain two instances of the generic program. These instances correspond to the computation of maximal graph components, viz. maximal independent sets of vertices and maximal sets of edges without cycles (i.e. maximal forests). Received: 29 May 1998 / 28 June 1999     

Techniques for fast instruction cache performance evaluation

Cache performance has become a very crucial factor in the overall system performance of machines. Effective analysis of a cache design requires the evaluation of the performance of the cache for typical programs that are to be executed on the machine. Recent attempts to reduce the time required for such evaluations either result in a loss of accuracy or require an initial pass by a filter to reduce the length of the trace. This paper evaluates techniques that attempt to overcome these problems for instruction cache performance evaluation. For each technique variations with and without periodic context switches are examined. Information calculated during the compilation is used to reduce the number of references in the trace. Thus, in effect references are stripped before the initial trace is generated. These techniques are shown to significantly reduce the time required for evaluating instruction caches with no loss of accuracy.     

Fully dynamic algorithms for permutation graph coloring

We introduce a dynamic model for maintaining permutation graph coloring. Our motivation comes from the strait type river routing problem in VLSI. This paper presents fully dynamic algorithms for the permutation graph coloring problem. These algorithms are designed to handle Insert and Delete operations and answer some queries. The aim is to provide for running times that are asymptotically more efficient than recomputation (off-line algorithms that run in 0(n logw) time, are known [5,6,10,3]). First, the algorithm A^ that runs in 0(n) uniform running time per Insert/Delete operation is presented. Second, a more sophisticated data structure leads to the algorithm A2 that runs in (9(m logw) uniform running time per Insert I Delete, where m denotes the number of chains in the decomposition. It follows from [7,4] that the running time of A2 when the points from the dynamically changing set are drawn independently from a uniform distribution on the unit square is G(yfn logn) per Insert/Delete in probability. Third, we sketch a composite algorithm A3 that switches between A± and A2 guarantees an amortized running time of (min{n,m logw)) per Insert/Delete. Finally, we outline a number of applications     

Errors in graph embedding algorithms

One major area of difficulty in developing an algorithm for embedding a graph on a surface is handling bridges which have more than one possible placement. This paper addresses a number of published algorithms where this has not been handled correctly. This problem arises in certain presentations of the Demoucron, Malgrange and Pertuiset planarity testing algorithm. It also occurs in an algorithm of Filotti for embedding 3-regular graphs on the torus. The same error appears in an algorithm for embedding graphs of arbitrary genus by Filotti, Miller and Reif. It is also present in an algorithm for embedding graphs of arbitrary genus by Djidjev and Reif. The omission regarding the Demoucron, Malgrange and Pertuiset planarity testing algorithm is easily remedied. However there appears to be no way of correcting the algorithms of the other papers without making the algorithms take exponential time.     

Efficient DNA sticker algorithms for NP-complete graph problems

Adleman's successful solution of a seven-vertex instance of the NP-complete Hamiltonian directed path problem by a DNA algorithm initiated the field of biomolecular computing. We provide DNA algorithms based on the sticker model to compute all k-cliques, independent k-sets, Hamiltonian paths, and Steiner trees with respect to a given edge or vertex set. The algorithms determine not merely the existence of a solution but yield all solutions (if any). For an undirected graph with n vertices and m edges, the running time of the algorithms is linear in n+m. For this, the sticker algorithms make use of small combinatorial input libraries instead of commonly used large libraries. The described algorithms are entirely theoretical in nature. They may become very useful in practice, when further advances in biotechnology lead to an efficient implementation of the sticker model.     

Constraint programming and graph algorithms

Aconstraint system includes a set of variables and a set of relations among these variables, calledconstraints. The solution of a constraint system is an assignment of values to variables so that all, or many, of the relations are made true. A simple and efficient method for constraint resolution has been proposed in the work of B.N. Freeman-Benson, J. Maloney, and A. Borning. We show how their method is related to the classical problem of graph matching, and from this connection we derive new resolution algorithms.     

Space efficient algorithms for some graph theoretical problems

Summary We present space-efficient-O(log² n)-deterministic algorithms for some graph theoretical problems such as planarity testing, producing a plane embedding, finding minimum cost spanning trees, obtaining the connected, biconnected and triconnected components of a graph. Previous planarity algorithms used (n) space. Several algorithms are based on a space-efficient matrix inversion method. The same bounds hold for uniform circuit depth.Research partially supported by NSF grants No. MCS 79-05006 and MCS 78-27600.     

Parallel bioinspired algorithms for NP complete graph problems

It is no longer believed that DNA computing will outperform digital computers when it comes to the computation of intractable problems. In this paper, we emphasise the in silico implementation of DNA-inspired algorithms as the only way to compete with other algorithms for solving NP-complete problems. For this, we provide sticker algorithms for some of the most representative NP-complete graph problems. The simple data structures and bit-vertical operations make them suitable for some parallel architectures. The parallel algorithms might solve either moderate-size problems in an exact manner or, when combined with a heuristic, large problems in polynomial time.     

基于最小价值的流媒体缓存替换算法

为提高基于P2P流媒体系统的服务质量,提出了一种基于最小价值的流媒体缓存替换算法SDU.研究了现有的缓存替换算法,通过对现有的缓存替换算法的理解、研究和分析,得出了现有的缓存替换算法在P2P网络节点间效率不高.对P2P网络和流媒体系统的分析研究,提出了SDU算法.该算法综合考虑了副本的供求关系、数据的紧迫度和数据的字节...