The edge of the Internet is increasingly becoming wireless. Therefore, monitoring the wireless edge is important to understanding the security and performance aspects of the Internet experience. We designed and implemented a large-scale WLAN monitoring system, the Dartmouth Internet security testbed (DIST), at Dartmouth College. It is equipped with distributed arrays of "sniffers" that cover 210 diverse campus locations and more than 5,000 users. In this paper, we describe our approach, designs, and solutions for addressing the technical challenges that have resulted from efficiency, scalability, security, and management perspectives. We also present extensive evaluation results on a production network, and summarize the lessons learned.

System R's bottom-up query optimizer architecture forms the basis of most current commercial database managers. The paper compares the performance of top-down and bottom-up optimizers, using the measure of the number of plans generated during optimization. Top down optimizers are superior according to this measure because they can use upper and lower bounds to avoid generating groups of plans. Early during the optimization of a query, a top-down optimizer can derive upper bounds for the costs of the plans it generates. These bounds are not available to typical bottom-up optimizers since such optimizers generate and cost all subplans before considering larger containing plans. These upper bounds can be combined with lower bounds, based solely on logical properties of groups of logically equivalent subqueries, to eliminate entire groups of plans from consideration. We have implemented such a search strategy, in a top-down optimizer called Columbia. Our performance results show that the use of these bounds is quite effective, while preserving the optimality of the resulting plans. In many circumstances this new search strategy is even more effective than heuristics such as considering only left deep plans.

In this presentation, we will describe a collection of new object-relational features that have been added to IBM's DB2 Universal Database (UDB) system. The features to be described include support for structured types, object references, and hierarchies of typed tables and views. These features will be covered from the perspective of a database designer or end user. In addition to presenting the features presently available in DB2 UDB V5.2, which became available in Fall 1998, we will discuss the expected evolution and impact of this technology over time.

Query optimizers often limit the search space for join orderings, for example by excluding Cartesian products in subplans or by restricting plan trees to left-deep vines. Such exclusions are widely assumed to reduce optimization effort while minimally affecting plan quality. However, we show that searching the complete space of plans is more affordable than has been previously recognized, and that the common exclusions may be of little benefit.We start by presenting a Cartesian product optimizer that requires at most a few seconds of workstation time to search the space of bushy plans for products of up to 15 relations. Building on this result, we present a join-order optimizer that achieves a similar level of performance, and retains the ability to include Cartesian products in subplans wherever appropriate. The main contribution of the paper is in fully separating join-order enumeration from predicate analysis, and in showing that the former problem in particular can be solved swiftly by novel implementation techniques. A secondary contribution is to initiate a systematic approach to the benchmarking of join-order optimization, which we apply to the evaluation of our method.

Scientific applications are infrequent users of commercial database management systems. We feel that a key reason is they do not offer good support for ordered data structures, such as multidimensional arrays, that are needed for natural representation of many scientific data types. In this papers, we lay out issues in database support of ordered structures, consider possible approaches along with their advantages and shortcomings, and direct the reader to the wide variety of prior work outside the data management field that might be successfully applied in this endeavor.