Prefetching Based on Type-Level Access Pattern in Object-Relational DBMSs

Prefetching is an effective method for minimizing the number of round-trips between the client and the server in database management systems. In this paper; we propose new notions of the typelevel access locality and the type-level access pattern. We also formally define the notions of capturing and prefetching to help understand the underlying mechanisms. We then develop an efJicient prefetching policy based on these notions and the framework. The type-level access locality is a pheonomenon that repetitive patterns exist in the attributes referenced. The type-level access pattern is a pattern of attributes that are referenced in accessing the objects. Existing prefetching methods are based on object-level or page-level access patterns, which consist of object-ids or page-ids of the objects accessed. Howevel; the drawback of these methods is that they work only when exactly the same objects or pages are accessed repeatedly. In contrast, even though the same objects are not accessed repeatedly, our technique effectively prefetches objects if the same attributes are referenced repeatedly, i.e.. if there is type-level access locality. Many navigational applications in Object-Relational Database Management Systems(0RDBMSs) have type-level access locality. Therefore, our technique can be employed in ORDBMSs to effectively reduce the number of roundtrips, thereby significantly enhancing the performance. We have conducted extensive experiments in a prototype ORDBMS to show the effectiveness of our algorithm. Experimental results using the 007 benchmark and a real GIS application show that our technique provides orders of magnitude improvements in roundtrips and several factors of improvements in overall performance over on-demand fetching and context-based prefetching, which is a state-of-the-art prefetching method. These results indicate that our approach provides a new paradigm in prefetching that improves pe$omance of navigational applications significantly and is a practical method that can be implemented in commercial OR-