Showing papers by "Anthony Tomasic published in 1996"

Scaling heterogeneous databases and the design of Disco

Abstract: Access to large numbers of data sources introduces new problems for users of heterogeneous distributed databases. End users and application programmers must deal with unavailable data sources. Database administrators must deal with incorporating new sources into the model. Database implementers must deal with the translation of queries between query languages and schemas. The Distributed Information Search COmponent (Disco) addresses these problems. Query processing semantics are developed to process queries over data sources which do not return answers. Data modeling techniques manage connections to data sources. The component interface to data sources flexibly handles different query languages and translates queries. This paper describes (a) the distributed mediator architecture of Disco, (b) its query processing semantics, (C) the data model and its modeling of data source connections, and (d) the interface to underlying data sources.

Scrambling query plans to cope with unexpected delays

Abstract: Accessing data from numerous widely distributed sources poses significant new challenges for query optimization and execution. Congestion and failures in the network can introduce highly variable response times for wide area data access. The paper is an initial exploration of solutions to this variability. We introduce a class of dynamic, run time query plan modification techniques that we call query plan scrambling. We present an algorithm that modifies execution plans on-the-fly in response to unexpected delays in obtaining initial requested tuples from remote sources. The algorithm both reschedules operators and introduces new operators into the query plan. We present simulation results that demonstrate how the technique effectively hides delays by performing other useful work while waiting for missing data to arrive.

Performance issues in distributed shared-nothing information-retrieval systems

Abstract: Many information-retrieval systems provides access to abstracts. For example, Stanford University, through its FOLIO system, provides access to the INSPEC database of abstracts of the literature on physics, computer science, electrical engineering, etc. In this article, this database is studied by using a trace-driven simulation. It focuses on a physical-index design that accommodates truncations, inverted-index caching, and database scaling in a distributed shared-nothing system. All three issues are shown to have a strong effect on response time and throughput. Database scaling is explored in two ways. One way assumes an “optimal” configuration for a single host and then linearly scales the database by duplicating the host architecture as needed. The second way determines the optimal number of hosts given a fixed database size.