Efficient methods of processing unanticipated queries are a crucial prerequisite for the success of generalized database management systems. A wide variety of approaches to improve the performance of query evaluation algorithms have been proposed: logic-based and semantic transformations, fast implementations of basic operations, and combinatorial or heuristic algorithms for generating alternative access plans and choosing among them. These methods are presented in the framework of a general query evaluation procedure using the relational calculus representation of queries. In addition, nonstandard query optimization issues such as higher level query evaluation, query optimization in distributed databases, and use of database machines are addressed. The focus, however, is on query optimization in centralized database systems.

Abstract- A theoretical approach to the optimal design of a large multifile'physical database is presented. The design algorithm is based on the theory that, given a set of join methods that satisfy a certain property called separability, the problem of optimal assignment of access structures to the whole database can be reduced to the subproblem of optimizing individual relations independently of one another. Coupling factors are defined to represent all the interactions among the relations. This approach not only reduces the complexity of the problem significantly, but also provides a better understanding of underlying mechanisms. Index Terms-Block accesses, index selection, join methods, physical database design, query optimization, selectivity. I.

The number of processor cache misses has a critical impact on the performance of DBMSs running on servers with large main-memory configurations.

A model of database storage and access is presented. The model represents many evaluation algorithms as special cases, and helps to break a complex algorithm into simple access operations. Generalized access cost equations associated with the model are developed and analyzed. Optimization of these cost equations yields an optimal access algorithm which can be synthesized by a query subsystem whose design is based on the modular access operations.

this paper, we apply this concept of non-equivalent query rewriting to the problem of maintaining view definitions (data warehouses), where it now allows us to handle a much larger class of changes of the underlying information sources, namely not only data but also schema changes. This relaxed query notion allows for more diversity in acceptable query answers, but also raises a new issue of the evaluation of such queries. For this purpose, we introduce an analytical model of query rewritings that incorporates measures of information preservation (quality) of a query in addition to the commonly studied measures of view maintenance performance (query cost). Quality is modeled as a function of the divergence from the intended view extent, both in terms of the preservation of the information amount and the information type. Both quality and cost are integrated into one uniform model, called the Quality-CostModel or QC-Model, to allow for a trade-off among these two measures. This model can be used to compare two alternate (even if not equivalent) rewritings, and thus to automatically select a good view maintenance solution from among numerous non-equivalent rewritings. We also report on an experimental evaluation of our model on a real testbed implementing distributed data warehouse maintenance, which supports the accuracy of the predictions of our model. This testbed also allows us to empirically determine important model parameters in an experimental implementation. Keywords: Relaxed query semantics, non-equivalent view maintenance, data warehouse, cost model, information description, evolving information sources, rewriting views.

Materialized views (data warehouses) are becoming increasingly important in the context of distributed modern environments such as the World Wide Web. Information sources (ISs) in such an environment may change their capabilities (schema). This causes a data warehouse defined by view queries over distributed sources to become undefined. Algorithms have been proposed to evolve (rewrite) view queries after capability changes of ISs by exploiting meta-descriptions about ISs and their relationships. This view rewriting process is referred to as view synchronization. View synchronization algorithms generate a potentially large number of valid solutions for the rewriting of a view query. Our analysis, as presented in this paper, shows that the most expressive algorithm for view synchronization has very high complexity (in O(n!)). The objective of this current work is hence to propose optimizations for this view synchronization process in order to make it practically usable. For this, we iden...

this paper we use the term access to mean the aggregate of access structures assigned to a relation or to the whole database. Most past research directed toward optimal design of physical databases has on single-file cases. This research must be extended to the design of the configuration of multifile databases. Although some efforts have been devoted to cases [GAM [BAT [KAT the approaches employed fall far short of accomplishing automatic design of optimal physical databases. In this paper we discuss issues involved in designing the access configuration of a physical database so as to minimize the of disk accesses for queries and updates. Our approach is formal and deliberately avoiding on heuristics. Our is to the whole of underlying By analyzing an important set of join methods the property we call we shall prove that optimal design of the access configuration of a multifile can be reduced to optimal of individual relations. In this WC restrict the join to this to the SEPARABILITY AS A PIIYSICAL DATABASE DESIGN METHODOLOGY whole approach formally manageable. Extensions to other join methods will be mentioned briefly. The main idea is to set up a basic design in accordance with a formal method that includes a large subset of practically important join methods, and then, using some straightforward heuristics, extend this basic design methodology to include other join methods as well. Section 1.2 introduces several key assumptions, while Section 1.3 applicable join methods of interest. In Section 1.5, the design theory will be developed by using the simple cost model introduced for the examples in Section 1.4. A design algorithm based on the theory will be introduced in Section 1.6

1.1 General Remarks............................ 3