Emerging database application domains demand not only new functionality but also high performance. To satisfy these two requirements, the Volcano project provides efficient, extensible tools for query and request processing, particularly for object-oriented and scientific database systems. One of these tools is a new optimizer generator. Data model, logical algebra, physical algebra, and optimi-zation rules are translated by the optimizer generalor into optimizer source code. Compared with our earlier EX-ODUS optimizer generator prototype, the search engine is more extensible and powerful; it provides effective support for non-trivial cost models and for physical properties such as sort order. At the same time, it is much more efficient as it combines dynamic programming, which until now had been used only for relational select-project-join optimization, with goal-directed search and branch-and-bound pruning. Compared with other rule-based optimi-zation systems, it provides complete data model indepen-dence and more natural extensibility. 1.

One of the basic functionalities of database management systems (DBMSs) is to be able to process declarative user queries. The first generation of object-oriented DBMSs did not provide declarative query capabilities. However, the last decade has seen significant research in defining query models (including calculi, algebra and user languages) and in techniques for processing and optimizing them. Many of the current commercial systems provide at least rudimentary query capabilities. In this chapter we discuss the techniques that have been developed for processing object-oriented queries. Our particular emphasis is on extensible query processing architectures and techniques. The other chapters in this book on query languages and optimization techniques complement this chapter. 1

In the past few years, query languages featuring generalized path expressions have been proposed. These languages allow the interrogation of both data and structure. They are powerful and essential for a number of applications. However, until now, their evaluation has relied on a rather naive and inefficient algorithm. In this paper, we extend an object algebra with two new operators and present some interesting rewriting techniques for queries featuring generalized path expressions. We also show how a query optimizer can integrate the new techniques. 1 Introduction In the past few years there has been a growing interest in query languages featuring generalized path expressions (GPE) [BRG88, KKS92, CACS94, QRS + 95]. With these languages, one may issue queries on data without exact knowledge of its structure. A GPE queries data and structure at the same time. Although very useful for standard database applications, these languages are vital for new applications dedicated, for insta...

The Decomposition Storage Model (DSM) vertically partitions all attributes of a given relation. DSM has excellent I/O behavior when the number of attributes touched in the query is small. It also has a better cache footprint than the N-ary storage model (NSM) that is used by most database systems. However, DSM incurs a high cost in reconstructing the original tuple from the partitions. We first revisit some of the performance problems associated with DSM. We suggest a simple indexing strategy and compare different reconstruction algorithms. The paper then proposes a new mirroring scheme, termed fractured mirrors, using both NSM and DSM models. This scheme combines the best aspects of both models, along with the added benefit of mirroring to better serve an ad-hoc query workload. A prototype system has been built using the Shore storage manager and performance is evaluated using queries from the TPCH workload.

In this work, we propose and assess a technique called bypass processing for optimizing the evaluation of disjunctive queries with expensive predicates. The technique is particularly useful for optimizing selection predicates that contain terms whose evaluation costs vary tremendously; e.g., the evaluation of a nested subquery or the invocation of a user-defined function in an object-oriented or extended relational model may be orders of magnitude more expensive than an attribute access (and comparison). The idea of bypass processing consists of avoiding the evaluation of such expensive terms whenever the outcome of the entire selection predicate can already be induced by testing other, less expensive terms. In order to validate the viability of bypass evaluation, we extend a previously developed optimizer architecture and incorporate three alternative optimization algorithms for generating bypass processing plans. 1 Introduction During the past few years we have witnessed tremendous...

Distributed databases operating over wide-area networks such as the Internet, must deal with the unpredictable nature of the performance of communication. The response times of accessing remote sources can vary widely due to network congestion, link failure, and other problems. In such an unpredictable environment, the traditional iterator-based query execution model performs poorly. We have developed a class of methods, called query scrambling, for dealing explicitly with the problem of unpredictable response times. Query scrambling dynamically modifies query execution plans on-the-fly in reaction to unexpected delays in data access. In this paper we focus on the dynamic scheduling of query operators in the context of query scrambling. We explore various choices for dynamic scheduling and examine, through a detailed simulation, the effects of these choices. Our experimental environment considers pipelined and non-pipelined join processing in a client with multiple remote data sources ...

There is already a sizable body of proposals on OODB query optimization. One of the most challenging problems in this area is query unnesting, where the embedded query can take any form, including aggregation and universal quantification. Although there is already a number of proposed techniques for query unnesting, most of these techniques are applicable to only few cases. We believe that the lack of a general and simple solution to the query unnesting problem is due to the lack of a uniform algebra that treats all operations (including aggregation and quantification) in the same way. This paper presents a new query unnesting algorithm that generalizes many unnesting techniques proposed recently in the literature. Our system is capable of removing any form of query nesting using a very simple and efficient algorithm. The simplicity of the system is due to the use of the monoid comprehension calculus as an intermediate form for OODB queries. The monoid comprehension calculus treats op...

Although scientific data analysis increasingly requires access and manipulation of large quantities of data, current database technology fails to meet the needs of scientific processing in a number of areas. To overcome acceptance problems among scientific users, database systems must provide performance and functionality comparable to current combinations of scientific programs and file systems. Therefore, we propose extending the concept of a database query to include numeric computation over scientific databases. In this paper, we examine the specification of an integrated algebra that includes traditional database operators for pattern matching and search as well as numeric operators for scientific data sets. Through the use of a single integrated algebra, we can perform automatic optimization on scientific computations, realizing all of the traditional benefits of optimization. We have experimented with a prototype optimizer which integrates sets, time series and spectra data types and operators on those types. Our results demonstrate that scientific database computations using numeric operators on multiple data types can’be effectively optimized and permit performance gains that could not be realized without the integration, This research has been performed in collaboration with the Space Grant College at the University of Colorado at Boulder, where the results are being applied to the analysis of experimental data from satellite observations. 1.

Paper Number 323 In this paper we describe the design and implementation of OPT++, a tool for Extensible Database Query Optimization that uses an object-oriented design to simplify the task of implementing, extending, and modifying an optimizer. Building an optimizer using OPT++ makes it easy to extend the query algebra (to add new query algebra operators and physical implementation algorithms to the system), easy to change the search space explored, and also easy to change the search strategy used. Furthermore, OPT++ comes equipped with a number of search strategies that are available for use by an Optimizer{ Implementor. OPT++ considerably simpli es both, the task of implementing an optimizer for a new database system, and the task of experimenting with various optimization techniques and strategies to decide what techniques are best suited for that database system. We present the results of performance studies which validate our design and show that, in spite of its exibility, OPT++ can be used to build e cient optimizers. 1

. Numerous structures for database query optimizers have been proposed. Many of those proposals aimed at automating the construction of query optimizers from some kind of specification of optimizer behavior. These specification frameworks do a good job of partitioning and modularizing the kinds of information needed to generate a query optimizer. Most of them represent at least part of this information in a rule-like form. Nevertheless, large portions of these specifications still take a procedural form. The contributions of this work are threefold. We present a language for specifying optimizers that captures a larger portion of the necessary information in a declarative manner. This language is in turn based on a model of query rewriting where query expressions carry annotations that are propagated during query transformation and planning. This framework is reminiscent of inherited and synthesized attributes for attribute grammars, and we believe it is expressive of a wide range of i...