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This study proposes a flexible and effective solution for developing high-performance multistage interconnection networks to maximize the performance of parallel computer systems, cloud computing infrastructure, grids, etc. An omega-type multistage interconnection network, consisting of regulated switchboxes, is used as a testbed to handle flexible two-class load patterns. The wormhole routing method and a special forwarding technique controlled by a global regulator are adopted to alleviate internal 'tree saturation' caused by periodic hotspot traffic combined with uniform traffic. Simulation experiments prove that this concept reduces packet latency, and an additional layer inserted in the final stage further improves the network's architecture. [ABSTRACT FROM AUTHOR]

Snapshot Isolation (SI) is a multiversion concurrency control algorithm, first described in Berenson et al. [1995]. SI is attractive because it provides an isolation level that avoids many of the common concurrency anomalies, and has been implemented by Oracle and Microsoft SQL Server (with certain minor variations). SI does not guarantee serializability in all cases, but the TPC-C benchmark application [TPC-C], for example, executes under SI without serialization anomalies. All major database system products are delivered with default nonserializable isolation levels, often ones that encounter serialization anomalies more commonly than SI, and we suspect that numerous isolation errors occur each day at many large sites because of this, leading to corrupt data sometimes noted in data warehouse applications. The classical justification for lower isolation levels is that applications can be run under such levels to improve efficiency when they can be shown not to result in serious errors, but little or no guidance has been offered to application programmers and DBAs by vendors as to how to avoid such errors. This article develops a theory that characterizes when nonserializable executions of applications can occur under SI. Near the end of the article, we apply this theory to demonstrate that the TPC-C benchmark application has no serialization anomalies under SI, and then discuss how this demonstration can be generalized to other applications. We also present a discussion on how to modify the program logic of applications that are nonserializable under SI so that serializability will be guaranteed. Categories and Subject Descriptors: H.2.4 [Database Management]: Systems--Transaction processing General Terms: Theory, Reliability Additional Key Words and Phrases: Concurrency control, serializability, anomaly, consistency, weak isolation, snapshot isolation, multiversion concurrency

We present HISTEX, a tool for testing the implementation of isolation levels of relational database management systems. It is a multiprocess application and executes input histories in a generic transactional notation on commercial DBMS platforms. HISTEX could be used to discover potential errors in the implementation of Isolation Levels by Relational Database Management Systems or cases where a system behaves over restrictively. It can also be used for performance measurements related to database workloads executing on real database systems instead of simulated environments. HISTEX has been implemented in C by utilizing Embedded SQL. However, many of its ideas could be reincarnated in new implementations that could rely on other database connectivity paradigms such as JDBC, JPA etc. We expect that by presenting some of the ideas behind its development we could re-invigorate some fresh interest and involvement in the research community regarding such tools.. [ABSTRACT FROM AUTHOR]