Algorithms for deferred view maintenance

TLDR

Materialized views are essential in data warehouses and similar applications, yet immediate maintenance imposes heavy overhead, so deferred maintenance is often preferred. The study proposes new algorithms for incremental refresh of materialized views during deferred maintenance. The algorithms employ auxiliary tables recorded since the last refresh, with three invariant‑based scenarios that control per‑transaction overhead and refresh time while avoiding a prior state‑bug limitation. Experiments show that selecting appropriate auxiliary tables reduces both per‑transaction overhead and view refresh time.

Abstract

Materialized views and view maintenance are important for data warehouses, retailing, banking, and billing applications. We consider two related view maintenance problems: 1) how to maintain views after the base tables have already been modified, and 2) how to minimize the time for which the view is inaccessible during maintenance.Typically, a view is maintained immediately, as a part of the transaction that updates the base tables. Immediate maintenance imposes a significant overhead on update transactions that cannot be tolerated in many applications. In contrast, deferred maintenance allows a view to become inconsistent with its definition. A refresh operation is used to reestablish consistency. We present new algorithms to incrementally refresh a view during deferred maintenance. Our algorithms avoid a state bug that has artificially limited techniques previously used for deferred maintenance.Incremental deferred view maintenance requires auxiliary tables that contain information recorded since the last view refresh. We present three scenarios for the use of auxiliary tables and show how these impact per-transaction overhead and view refresh time. Each scenario is described by an invariant that is required to hold in all database states. We then show that, with the proper choice of auxiliary tables, it is possible to lower both per-transaction overhead and view refresh time.