Rethinking Database Updates using a Multiple Assignment-based Approach

摘要

We investigate the problems involved in efficient implementation of multiple assignment to database tables, as suggested by Date and Darwen in their Third Manifesto proposal for future database systems [10]. We explain the connection between assignment and the INSERT, DELETE and UPDATE operations and why multiple assignments executed simultaneously are preferable to deferred constraint checking. Our contributions are twofold. Firstly, we enable the user to specify updates either in terms of the changes needed to the existing state or as the final table contents directly, with no degradation in performance. Secondly, when multiple tables are updated SQL places the responsibility on the user to order the update statements correctly. Integrity constraints must either be preserved in the unnecessary intermediate states or else deferred. Multiple assignment accepts updates across the entire database simultaneously and makes the system responsible for scheduling them correctly. We present methods for a proposed implementation that can potentially exceed the performance of SQL DBMSs by employing parallelism and multi-query optimization.