No abstract

In current Java implementations, Flemote Method Invocation (RMI) is too slow, especially for high performance computing. RMI is designed for wide-area and high-latency networks, it is based on a slow object serialization, and it does not support high-performance communication networks. The paper demonstrates that a much faster drop-in RMI and an efficient serialization can be designed and implemented completely in Java without any native code. Moreover, the re-designed RMI supports non-TCP/IP communication networks, even with heterogeneous transport protocols. As a by-product,, a benchmark collection for RMI is presented. This collection -asked -for by the Java Grande Forum from its first meeting -can guide JVM vendors in their performance optimizations.On PCs connected through Ethernet, the better serialization and the improved RMI save a median of 45% (maximum of 71%) of the runtime for :some set of arguments. On our Myrinet-based ParaStation network (a cluster of DEC Alphas) we save a median of 85% (maximum of 96%), compared to standard RMI, standard serialization, and Fast Ethernet; a remote method invocation runs as fast as 115 /.s round trip time, compared to about 1.5 ms.

ÐUsing design patterns is claimed to improve programmer productivity and software quality. Such improvements may manifest both at construction time (in faster and better program design) and at maintenance time (in faster and more accurate program comprehension). This paper focuses on the maintenance context and reports on experimental tests of the following question: Does it help the maintainer if the design patterns in the program code are documented explicitly (using source code comments) compared to a well-commented program without explicit reference to design patterns? Subjects performed maintenance tasks on two programs ranging from 360 to 560 LOC including comments. Both programs contained design patterns. The controlled variable was whether the use of design patterns was documented explicitly or not. The experiments thus tested whether pattern comment lines (PCL) help during maintenance if patterns are relevant and sufficient program comments are already present. It turns out that this question is a challenge for the experimental methodology: A setup leading to relevant results is quite difficult to find. We discuss these issues in detail and suggest a general approach to such situations. The experiment was performed with Java by 74 German graduate students and then repeated with C++ by 22 American undergraduate students. A conservative analysis of the results supports the hypothesis that pattern-relevant maintenance tasks were completed faster or with fewer errors if redundant design pattern information was provided. Redundant means that the information carried in pattern comments is also available in different form in other comments. The contribution of this article is twofold: It provides the first controlled experiment results on design pattern usage and it presents a solution approach to an important class of experiment design problems for experiments regarding documentation.

Abstract. Several new miners for frequent subgraphs have been published recently. Whereas new approaches are presented in detail, the quantitative evaluations are often of limited value: only the performance on a small set of graph databases is discussed and the new algorithm is often only compared to a single competitor based on an executable. It remains unclear, how the algorithms work on bigger/other graph databases and which of their distinctive features is best suited for which database. We have re-implemented the subgraph miners MoFa, gSpan, FFSM, and Gaston within a common code base and with the same level of programming expertise and optimization effort. This paper presents the results of a comparative benchmarking that ran the algorithms on a comprehensive set of graph databases.

SUMMARYIn current Java implementations, Remote Method Invocation (RMI) is too slow, especially for highperformance computing. RMI is designed for wide-area and high-latency networks, it is based on a slow object serialization, and it does not support high-performance communication networks. The paper demonstrates that a much faster drop-in RMI and an efficient drop-in serialization can be designed and implemented completely in Java without any native code. Moreover, the re-designed RMI supports non-TCP/IP communication networks, even with heterogeneous transport protocols. We demonstrate that for high-performance computing some of the official serialization's generality can and should be traded for speed. As a by-product, a benchmark collection for RMI is presented. On PCs connected through Ethernet, the better serialization and the improved RMI save a median of 45% (maximum of 71%) of the runtime for some set of arguments. On our Myrinet-based ParaStation network (a cluster of DEC Alphas) we save a median of 85% (maximum of 96%), compared to standard RMI, standard serialization, and Fast Ethernet; a remote method invocation runs as fast as 80 µs round trip time, compared with about 1.5 ms. Copyright