An incremental access method for ViewCache: concept, algorithms, and cost analysis

• Authors: Nicholas Roussopoulos
• Venue: ACM Transactions on Database Systems (TODS)
• Year: 1991

A ViewCache is a stored collection of pointers pointing to records of underlying relations needed to materialize a view. This paper presents an Incremental Access Method (IAM) that amortizes the maintenance cost of ViewCaches over a long time period or indefinitely. Amortization is based on deferred and other update propagation strategies. A deferred update strategy allows a ViewCache to remain outdated until a query needs to selectively or exhaustively materialize the view. At that point, an incremental update of the ViewCache is performed. This paper defines a set of conditions under which incremental access to the ViewCache is cost effective. The decision criteria are based on some dynamically maintained cost parameters, which provide accurate information but require inexpensive bookkeeping. The IAM capitalizes on the ViewCache storage organization for performing the update and the materialization of the ViewCaches in an interleaved mode using one-pass algorithms. Compared to the standard technique for supporting views that requires reexecution of the definition of the view, the IAM offers significant performance advantages. We will show that under favorable conditions, most of which depend on the size of the incremental update logs between consecutive accesses of the views, the incremental access method outperforms query modification. Performance gains are higher for multilevel ViewCaches because all the I/O and CPU for handling intermediate results are avoided.