Øystein Torbjørnsen

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New telecommunication services and mobility networks have introduced databases in telecommunication networks. Compared with traditional use of databases, telecom databases must fulfill very tough requirements on response time, throughput, and availability. ClustRa is a telecom database prototype developed to run on standard workstations interconnected by an(More)
Bitmap indexes are widely used in Decision Support Systems (DSSs) to improve query performance. In this paper, we evaluate the use of compressed inverted indexes with adapted query processing strategies from Information Retrieval as an alternative. In a thorough experimental evaluation on both synthetic data and data from the Star Schema Benchmark, we show(More)
The thesis introduces the concept of multi-site declustering strategies with self repair for databases demanding very high service availability. Existing work on declustering strategies are centered around providing high performance and reliability inside a small geographical area (site). Applications demanding robustness against site failures like fire and(More)
This paper describes the architectures that can be used to build highly available database management systems. We describe these architectures along two dimensions – process redundancy and data redundancy. Process redundancy refers to the management of redundant processes that can take over in case of a process or node failure. Data redundancy refers to the(More)
XML indexing and search has become an important topic, and twig joins are key building blocks in XML search systems. This paper describes a novel approach using a nested loop twig join algorithm, which combines several existing techniques to speed up evaluation of XML queries. We combine structural summaries, path indexing and prefix path partitioning to(More)
In order to provide database availability in the presence of node and site failures, traditional l-safe algorithms disallow primary and hot standby replicas to be located at the same site. This means that the failure of a single primary node must be handled like a failure of the entire primary site. Furthermore, this excludes symmetric site configurations,(More)
Application Server is a standard middleware platform for deploying web-based business applications which typically require the underlying platform to deliver high system availability and to minimize loss of transactions. This paper presents a measurement-based availability modeling and analysis for a fault tolerant Application Server system – Sun Java(More)
A database for telecom applications must satisfy the same demanding requirements as the other components in the telecom network with respect to availability , scalability, and real-time performance. Unfortunately it is diicult to provide state-of-the-art real-time service without sacriicing the other. ClustRa is a parallel and distributed telecom DBMS(More)