The holy grail for database architecture research is to find a solution that is Scalable & Speedy, to run on anything from small ARM processors up to globally distributed compute clusters, Stable & Secure, to service a broad user community, Small & Simple, to be comprehensible to a small team of programmers, Self-managing, to let it run out-of-the-box without hassle. In this paper, we provide a trip report on this quest, covering both past experiences, ongoing research on hardware-conscious algorithms, and novel ways towards self-management specifically focused on column store solutions. 1.

A purely relational account of the true XQuery semantics can turn any relational database system into an XQuery processor. Compiling nested expressions of the fully compositional XQuery language, however, yields odd algebraic plan shapes featuring scattered distributions of join operators that currently overwhelm commercial SQL query optimizers. This work rewrites such plans before submission to the relational database back-end. Once cast into the shape of join graphs, we have found off-the-shelf relational query optimizers—the B-tree indexing subsystem and join tree planner, in particular—to cope and even be autonomously capable of “reinventing ” advanced processing strategies that have originally been devised specifically for the XQuery domain, e.g., XPath step reordering, axis reversal, and path stitching. Performance assessments provide evidence that relational query engines are among the most versatile and efficient XQuery processors readily available today.

Data warehouses underlying virtual observatories stress the capabilities of database management systems in many ways. They are filled, on a daily basis, with large amounts of factual information derived from intensive data scrubbing and computational feature extraction pipelines. The predominant data processing techniques focus on parallel loads and map-reduce feature extraction algorithms. Querying these huge databases require a sizable computing cluster, while ideally the initial investigation should run interactively, using as few resources as possible. In this paper, we explore a different route, one based on the observation that at any given time only a fraction of the data is of primary value for a specific task. This fraction becomes the focus of scientific reflection through an iterative process of ad-hoc query refinement. Steering through data to facilitate scientific discovery demands guarantees for the query execution time. In addition, strict bounds on errors are required to satisfy the demands of scientific use, such that query results can be used to test hypotheses reliably. We propose SciBORQ, a framework for scientific data exploration that gives precise control over runtime and quality of query answering. We present novel techniques to derive multiple interesting data samples, called impressions. An impression is selected such that the statistical error of a query answer remains low, while the result can be computed within strict time bounds. Impressions differ from previous sampling approaches in their bias towards the focal point of the scientific data exploration, their multi-layer design, and their adaptiveness to shifting query workloads. The ultimate goal is a complete system for scientific data exploration and discovery, capable of producing quality answers with strict error bounds in pre-defined time frames. 1.

Abstract. Traditional optimizers fail to pick good execution plans, when faced with increasingly complex queries and large data sets. This failure is even more acute in the context of XQuery, due to the structured nature of the XML language. To overcome the vulnerabilities of traditional optimizers, we have previously proposed ROX, a Run-time Optimizer for XQueries, which interleaves optimization and execution of full tables. ROX has proved to be robust, even in the presence of strong correlations, but it has one limitation: it uses full materialization of intermediate results making it unsuitable for pipelined systems. Therefore, this paper proposes ROX-sampled, a variant of ROX, which executes small data samples, thus generating smaller intermediates. We conduct extensive experiments which proved that ROX-sampled is comparable to ROX in performance, and that it is still robust against correlations. The main benefit of ROX-sampled is that it allows the large number of pipelined databases to import the ROX idea into their optimization paradigm. 1

in 1985. It has steadily grown from two PhD students to a group of 17 people ultimo 2011. The group is supported by a scientific programmer and