TAILIEUCHUNG - NiagaraCQ: A Scalable Continuous Query System for Internet Databases

Continuous queries are persistent queries that allow users to receive new results when they become available. While continuous query systems can transform a passive web into an active environment, they need to be able to support millions of queries due to the scale of the Internet. No existing systems have achieved this level of scalability. NiagaraCQ addresses this problem by grouping continuous queries based on the observation that many web queries share similar structures. Grouped queries can share the common computation, tend to fit in memory and can reduce the I/O cost significantly. Furthermore, grouping on selection predicates can eliminate a large number of unnecessary query invocations. Our grouping technique is distinguished. | NiagaraCQ A Scalable Continuous Query System for Internet Databases Jianjun Chen David J. DeWitt Feng Tian Yuan Wang Computer Sciences Department University of Wisconsin-Madison jchen dewitt ftian yuanwang @ ABSTRACT Continuous queries are persistent queries that allow users to receive new results when they become available. While continuous query systems can transform a passive web into an active environment they need to be able to support millions of queries due to the scale of the Internet. No existing systems have achieved this level of scalability. NiagaraCQ addresses this problem by grouping continuous queries based on the observation that many web queries share similar structures. Grouped queries can share the common computation tend to fit in memory and can reduce the I O cost significantly. Furthermore grouping on selection predicates can eliminate a large number of unnecessary query invocations. Our grouping technique is distinguished from previous group optimization approaches in the following ways. First we use an incremental group optimization strategy with dynamic re-grouping. New queries are added to existing query groups without having to regroup already installed queries. Second we use a query-split scheme that requires minimal changes to a general-purpose query engine. Third NiagaraCQ groups both change-based and timer-based queries in a uniform way. To insure that NiagaraCQ is scalable we have also employed other techniques including incremental evaluation of continuous queries use of both pull and push models for detecting heterogeneous data source changes and memory caching. This paper presents the design of NiagaraCQ system and gives some experimental results on the system s performance and scalability. 1. INTRODUCTION Continuous queries TGNO92 LPT99 LPBZ96 allow users to obtain new results from a database without having to issue the same query repeatedly. Continuous queries are especially useful in an environment like the Internet

• Quản trị mạng
• medicine availability
• private sector
• private pharmacies
• Regulatory Mechanism
• Asexual Cycles
• Terpenoids and Gibberellic
• Acids Interaction
• official opinion
• private sectors
• Photosynthesis
• Carotenoids and Photosynthesis
• Carotenoid Biosyntesis
• sector availability
• originator brand medicines
• generic products ranged
• Germin Gene Products
• Under Salt Stress
• Adaptation and Tolerance
• Report medicine
• traditional medicine
• scientific reports
• intermediate cells
• cell proliferation
• medical analysis
• comprehensive imple mentation
• stringent enforcement
• intention of regulation
• Root Produced
• Volatile Secondary
• Metabolites
• Mediating Soil Interactions
• Insulin Like Growth
• Based Approach
• New Therapeutics
• healthcare professionals
• patients is essential
• evidence based
• extent and nature
• reliable information
• prices and availability
• formulated and implemented
• Nutrition and Growth
• UV C Hormesis
• Relation to Some
• policy options are available
• equitable and sustainable
• Proteins and Enzymes
• Post Translational
• Nuclear Proteins
• ecall or difficulties
• Medicines adherence
• encouraging patients
• Salt Tolerance
• Harvested Fruits
• Fruits and Vegetables