Nobutatsu Nakamura

Virtual playground: architectures for a shared virtual world

1. ABSTRACT This paper describes a shared virtual world with four key goals: a reasonable economic model; low latency for world synchronization; a hospitable environment for users; and affordances for social interaction. The first goal is supported by examining economic issues related to the design of commercially viable 3D virtual environments including issues such as allowing use of currently developed Web based content. The second goal is supported by underlying network support that combines a mixed set of Internet protocols and a mixed model of a central server for universal resource management and multicast based transaction distribution. The final two goals are supported through architectural design patterns and a literature review of social issues and personal representation in virtual worlds.

A Flexible Replication Mechanism with Extended Database Connection Layers

It is vital to achieve a disaster recovery system that allows a backup site to take over a primary sites IT services while the primary site is down. We propose a flexible replication mechanism based on service requirements such as system performance, recovery time objective (RTO), and recovery point objective (RPO). For high flexibility, the mechanism controls the replication schedule by monitoring the applications database accesses in the database connection library and matching the accesses with previously registered access patterns. In our experiments, we confirmed that the proposed mechanism outperforms other existing mechanisms, especially in situations with network delays and packet losses

Database Transaction Management for High-Availability Cluster System

We propose a database transaction management framework that enables a database replication function to be added to existing cluster systems. This framework is generally applicable to various database products merely by replacing the database connection API library. In this framework, the enhanced database connection API library duplicates the transactions issued by clustered applications and issues them to the primary and backup databases while controlling the issue order for consistency between the two databases. We implemented the proposed framework on a database connection API library for Java and confirmed that the overhead caused by duplication and order control was smaller than the existing replication methods overhead