Performance issues in mid-sized relational database machines

Relational database systems have provided end users and application programmers with an improved working environment over older hierarchial and networked database systems. End users now use interactive query languages to inspect and manage their data. And application programs are easier to write and maintain due to the separation of physical data storage information from the application program itself. These and other benefits do not come without a price however. System resource consumption has long been the perceived problem with relational systems. The additional resource demands usually force computing sites to upgrade existing systems or add additional facilities. One method of protecting the current investment in systems is to use specialized hardware designed specifically for relational database processing. \u27Database Machines\u27 provide that alternative. Since the commercial introduction of database machines in the early 1980\u27s, both software and hardware vendors of relational database systems have claimed superior performance over competing products. Without a STANDARD performance measurement technique, the database user community has been flooded with benchmarks and claims from vendors which are immediately discarded by some competitors as being biased towards a particular system design. This thesis discusses the issues of relational database performance measurement with an emphasis on database machines, however; these performance issues are applicable to both hardware and software systems. A discussion of hardware design, performance metrics, software and database design is included. Also provided are recommended guidelines to use in evaluating relational database systems in lieu of a standard benchmark methodology

3P. A First Approach to a Domain Specific Language for Constructing Code Generators

The present work defines the components and architecture of a Domain-specific Language that takes advantage of patterns and common tasks performed by code generators based on relational databases. This DSL (Domain-specific Language) allows developers to easily and rapidly build and maintain custom code generators that meet their particular requirements instead of building them from scratch using general purpose programming languages, which is more expensive in terms of time. Current work includes the definition of the Code Generation Domain constrained to the transformation of relational models into applications source code, high level architecture and features models. The implementation of the DSL is a future work

Reasoning about distributed relational data and query evaluation

Large data sets are often stored distributedly to increase the reliability of systems and the efficiency of query evaluation in them. While some query operators -- like selections and projections -- are intrinsically conform with parallel evaluation, others -- like joins -- demand specific distribution patterns. For relational databases, a common approach to evaluate queries in parallel relies on the use of rather simple distribution patterns for binary joins and the computation of the query result according to some query plan, operator by operator. Often, this requires the redistribution of large intermediate results (possibly larger than the input and/or output) and thus may lead to unnecessary long processing times. Thus, especially in the last decade, more elaborate distribution patterns that depend on the whole query have been studied and shown to allow more efficient query evaluation in several cases by reducing the amount of communication between servers. Ameloot et al. have described a setting where query evaluation is studied for a broad range of distribution patterns. Their work focuses on problems to decide whether a query can be evaluated correctly under a given distribution pattern. More particularly, they have considered two problems: "parallel correctness", where the pattern is specified explicitly, and "parallel-correctness transfer", where the pattern is known to be appropriate for another query. This thesis comprises the author's contributions to the complexity-theoretical investigation of these problems for conjunctive queries (and extensions thereof). These contributions complement the main characterisations and some additional complexity results by Ameloot et al. Furthermore, this thesis contains some new characterisations for "polarised" queries. Via the characterisations, parallel correctness and parallel-correctness transfer can be translated into questions on the co-occurrences of certain facts, induced by the query, on some server. Such questions and others can be modelled by "distribution dependencies", a variant of the well-known tuple- and equality-generating dependencies. Modelling via these constraints allows a more general description of distribution patterns in distributed relational data. The third contribution of this thesis is the study of the implication problem for distribution dependencies, providing lower and upper bounds for some fragments