A Run-Time Based Technique to Optimize Queries in Distributed Internet Databases

A Run-Time Based Technique to Optimize Queries in Distributed Internet Databases

Latifur Khan, Arunkumar Ponnusamy, Dennis McLeod, Cyrus Shahabi
Copyright: © 2003 |Pages: 34
DOI: 10.4018/978-1-59140-063-9.ch007
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An adaptive probe-based optimization technique is developed and demonstrated in the context of an Internet-based distributed database environment. More and more common are database systems, which are distributed across servers communicating via the Internet where a query at a given site might require data from remote sites. Optimizing the response time of such queries is a challenging task due to the unpredictability of server performance and network traffic at the time of data shipment; this may result in the selection of an expensive query plan using a static query optimizer. We constructed an experimental setup consisting of two servers running the same DBMS connected via the Internet. Concentrating on join queries, we demonstrate how a static query optimizer might choose an expensive plan by mistake. This is due to the lack of a priori knowledge of the run-time environment, inaccurate statistical assumptions in size estimation, and neglecting the cost of remote method invocation. These shortcomings are addressed collectively by proposing a probing mechanism. Furthermore, we extend our mechanism with an adaptive technique that detects sub-optimality of a plan during query execution and attempts to switch to the cheapest plan while avoiding redundant work and imposing little overhead. We demonstrate that this probe technique can be extended in a client-server environment as a basis for choosing the right place for the execution of user defined functions (UDFs). An implementation of our run-time optimization technique for queries was constructed in the Java language and incorporated into an experimental setup. The results demonstrate the superiority of our probe-based optimization over a static optimization.

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