tailieunhanh - Advances in Database Technology- P12

Tham khảo tài liệu 'advances in database technology- p12', công nghệ thông tin, cơ sở dữ liệu phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Distributed Query Optimization by Query Trading Fragkiskos Pentaris and Yannis loannidis Department of Informatics and Telecommunications University of Athens Ilisia Athens 15784 Hellas Greece frank yannis @ Abstract. Large-scale distributed environments where each node is completely autonomous and offers services to its peers through external communication pose significant challenges to query processing and optimization. Autonomy is the main source of the problem as it results in lack of knowledge about any particular node with respect to the information it can produce and its characteristics. Internode competition is another source of the problem as it results in potentially inconsistent behavior of the nodes at different times. In this paper inspired by ecommerce technology we recognize queries and query answers as commodities and model query optimization as a trading negotiation process. Query parts and their answers are traded between nodes until deals are struck with some nodes for all of them. We identify the key parameters of this framework and suggest several potential alternatives for each one. Finally we conclude with some experiments that demonstrate the scalability and performance characteristics of our approach compared to those of traditional query optimization. 1 Introduction The database research community has always been very interested in large intranet-and internet-scale federations of autonomous databases as these seem to satisfy the scalability requirements of existing and future data management applications. These systems find the answer of a query by splitting it into parts sub-queries retrieving the answers of these parts from remote black-box database nodes and merging the results together to calculate the answer of the initial query 1 . Traditional query optimization techniques are inappropriate 2 3 4 for such systems as node autonomy and diversity result in lack of knowledge about any particular node with respect to the .