Wir stellen die Cluster-Architektur IBM Parallel Sysplex und ihren Einsatz zur Datenbank- und Transaktionsverarbeitung vor. Die Sysplex-Architektur ermöglicht die Nutzung von bis zu 32 Mehrprozessor-Großrechnern auf einem gemeinsamen Datenbestand, ohne Modifikation bestehender Anwendungen. Eine wesentliche Komponente ist die sogenannte Coupling Facility (CF), in der allen Rechnern zugängliche globale Datenstrukturen und globale Pufferbereiche verwaltet werden. Wir diskutieren, wie mit einer solchen „nahen“ Rechnerkopplung leistungskritische Cluster-Aufgaben zur Synchronisation und Kohärenzkontrolle gelöst werden. Leistungsuntersuchungen zeigen eine hohe Skalierbarkeit der Sysplex-Performance in praktischen Einsatzfällen.

We analyze citation frequencies for two main database conferences (SIGMOD, VLDB) and three database journals (TODS, VLDB Journal, Sigmod Record) over 10 years. The citation data is obtained by integrating and cleaning data from DBLP and Google Scholar. Our analysis considers different comparative metrics per publication venue, in particular the total and average number of citations as well as the impact factor which has so far only been considered for journals. We also determine the most cited papers, authors, author institutions and their countries.

Dynamic load balancing is a prerequisite for effectively utilizing large parallel database systems. Load balancing at different levels is required in particular for assigning transactions and queries as well as subqueries to nodes. Special problems are posed by the need to support both inter-transaction/query as well as intra-transaction/query parallelism due to conflicting performance requirements. We compare the major architectures for parallel database systems, Shared Nothing and Shared Disk, with respect to their load balancing potential. For this purpose, we focus on parallel scan and join processing in multi-user mode. It turns out that both the degree of query parallelism as well as the processor allocation should be determined in a coordinated way and based on the current utilization of critical resource types, in particular CPU and memory.

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So far only few performance studies on parallel object-relational database systems are available. In particular, the relative performance of relational vs. reference-based join processing in a parallel environment has not been investigated sufficiently. We present a performance study based on the BUCKY benchmark to compare parallel join processing using reference attributes with relational hash- and merge-join algorithms. In addition, we propose a data allocation scheme especially suited for object hierarchies and set-valued attributes.

For complex queries in parallel database systems, substantial amounts of data must be redistributed between operators executed on different processing nodes. Frequently, such intermediate results cannot be held in main memory and must be stored on disk. To limit the ensuing performance penalty, a data allocation must be found that supports parallel I/O to the greatest possible extent. In this paper, we propose declustering even self-contained units of temporary data processed in a single operation (such as individual buckets of parallel hash joins) across multiple disks. Using a suitable analytical model, we find that the improvement of parallel I/O outweighs the penalty of increased fragmentation.

Skew effects are a serious problem in parallel database systems, but the relationship between different skew types and load balancing methods is still not fully understood. We develop and compare two classifications of skew effects and load balancing strategies, respectively, to match their relevant properties. Our conclusions highlight the importance of highly dynamic scheduling to optimize both the complexity and the success of load balancing. We also suggest the tuning of database schemata as a new anti-skew measure.

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Anhand eines konkreten Einsatzbeispieles (Vorlesungsverzeichnis SS '971 des Instituts für Informatik der Universität Leipzig) wird ein auf einer objektorientierten Datenbank und SGML basierendes System für elektronisches Publizieren vorgestellt. Unter Verwendung einer einfachen Substitutionssprache lassen sich Layout-Informationen für SGML-Dokumente kodieren, die in mehrerenFormaten (z.B. HTML, LaTeX, ASCII) ausgegeben werden können. Passwortgeschützte Modifizierung von Dokumenten erfolgt direkt im Web. Dank Implementierung in Java ist das System äußerst portabel.