A Case Study on Array Query Optimisation

The development of applications involving multi-dimensional data sets on top of a RDBMS raises several difficulties that are not directly related to the scientific problem being addressed. In particular, an additional effort is needed to solve the mismatch existing between the array-based data model typical for such computations and the set-based data model provided by the RDMBS. The RAM (Relational Array Mapping) system fills this gap, silently providing a mapping layer between the two data models. As expected though, a naive implementation of such an automatic translation cannot compete with the efficiency of queries written by an experienced programmer. In order to make RAM a valid alternative to expensive and time-consuming hand-written solutions, this performance gap should be reduced. We study a real-world application aimed at the ranking of multimedia collections to assess the impact of different implementation strategies. The result of this study provides an illustrative outlook for the development of generally applicable optimisation techniques.