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Query Planning for Continuous Aggregation Queries over a Network of Data Aggregators

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Title Query Planning for Continuous Aggregation Queries over a Network of Data Aggregators
 
Creator GUPTA, R
RAMAMRITHAM, K
 
Subject Algorithms
continuous queries
distributed query processing
data dissemination
coherency
performance
 
Description Continuous queries are used to monitor changes to time varying data and to provide results useful for online decision making. Typically a user desires to obtain the value of some aggregation function over distributed data items, for example, to know value of portfolio for a client; or the AVG of temperatures sensed by a set of sensors. In these queries a client specifies a coherency requirement as part of the query. We present a low-cost, scalable technique to answer continuous aggregation queries using a network of aggregators of dynamic data items. In such a network of data aggregators, each data aggregator serves a set of data items at specific coherencies. Just as various fragments of a dynamic webpage are served by one or more nodes of a content distribution network, our technique involves decomposing a client query into subqueries and executing subqueries on judiciously chosen data aggregators with their individual subquery incoherency bounds. We provide a technique for getting the optimal set of subqueries with their incoherency bounds which satisfies client query's coherency requirement with least number of refresh messages sent from aggregators to the client. For estimating the number of refresh messages, we build a query cost model which can be used to estimate the number of messages required to satisfy the client specified incoherency bound. Performance results using real-world traces show that our cost-based query planning leads to queries being executed using less than one third the number of messages required by existing schemes.
 
Publisher IEEE COMPUTER SOC
 
Date 2014-10-16T13:11:53Z
2014-10-16T13:11:53Z
2012
 
Type Article
 
Identifier IEEE TRANSACTIONS ON KNOWLEDGE AND DATA ENGINEERING, 24(6)1065-1079
http://dx.doi.org/10.1109/TKDE.2011.12
http://dspace.library.iitb.ac.in/jspui/handle/100/15633
 
Language en