AJAX - Adaptive Join Algorithm for Extreme Restrictions.

In a mobile ad hoc network (MANET), the nodes represent mobile computers in which database systems may reside. Such mobile computers (nodes) are free to move arbitrarily. In such an environment, we may have a collection of autonomous, distributed, heterogeneous and mobile databases (denoted Mobile Database Community or MDBC). Thus, each database user (in a mobile host) can access databases belonging to an MDBC through the MANET. Traditional query processing techniques fail to support the access to databases in an MDBC, since data delivery rate in such an environment becomes unpredictable and mobile hosts may suffer from limited available main memory to process some query operators (e.g., join). To react to those events, this paper presents an adaptive join operator, called AJAX, for processing join operations on mobile databases in an MDBC. AJAX ensures: (i) incremental production of results as soon as the data become available; (ii) progress of the query processing even when the delivery of data is blocked, and; (iii) reaction to situations of memory limitation on the execution of operator. Cost estimation and experimental results are presented to evidence that AJAX is an effective solution for processing join operation on mobile databases.