Incremental View Maintenance By Base Relation Tagging in Distributed Databases

Abstract

The incremental view maintenance problem deals with the efficient updating of materialized views in response to updates to base relations. This paper considers the problem in a distributed database environment, with communication cost minimization as the primary objective. The views considered are defined based on the relational join operation. The approach is to use “yes”/“no” tags as auxiliary data on tuples in the base relations to indicate whether the tuples participate in joins. These tags will help avoid sending irrelevant data over the network and thus reduce the communication cost. Two basic view maintenance algorithms are proposed using the tags. In addition to reducing communication costs, an important feature of these two basic algorithms is that they derive the “exact change” to views without looking at the old views. This feature allows us to maintain certain aggregates on views without actually materializing the views themselves; this feature is useful in applications such as active databases where many conditions or constraints must be tested whenever updates occur, since a condition is true exactly when some corresponding view has nonzero number of tuples. The paper then combines the use of tags with the counting algorithm to derive a tagged counting algorithm that further reduces the communication cost. The paper illustrates the algorithms by examples and studies their performance via a statistical analysis. The illustrating examples and the performance analysis show that, under uniform distribution with reasonable join participation rates, the use of tags significantly improves the efficiency of view maintenance over similar algorithms without tags. The performance analysis also identifies the situations where a particular algorithm is superior to others. The use of tags for memoing values of subexpressions in a view definition is also explored in the paper.