Performance modeling and access methods for temporal database management systems
Ilsoo Ahn · 1986
Conventional databases storing only the latest snapshot lack the capability to record and process time-varying aspects of the real world. The need for temporal support has been recognized for over ten years, and recent progress in secondary storage technology is making such support practically feasible. There are three distinct kinds of time in databases: transaction time, valid time, and user-defined time. Depending on the capability to support either or both of transaction time and valid time, databases are classified into four types: snapshot, rollback, historical, and temporal. Each of the four types has different semantics and different implementation issues. Database systems with temporal support maintain history data on line together with current data, which causes problems in terms of both space and performance. This research investigates the temporally partitioned store to provide fast response for various temporal queries without penalizing conventional non-temporal queries. The current store holds current data and possibly some history data, while the history store contains the rest. The two stores can utilize different storage formats, and even different storage media, depending on the individual data characteristics. Various issues on the temporally partitioned store were studied, and several formats for the history store were investigated. To analyze the performance of TQuel queries on various access methods, four models forming a hierarchy were developed: one each for algebraic expressions, database/relations, access paths, and storage devices. The model of algebraic expressions maps the algebraic expression to the file primitive expression, based on information represented by the model of database/relations. The model of access paths maps the file primitive expression to the access path expression, which is converted to the access path cost by the model of storage devices. As a test-bed to evaluate the access methods and the models, a prototype of a temporal DBMS was built by modifying a snapshot DBMS. The prototype was used to identify problems with conventional access methods and also to provide performance data to check the analysis results from the models. Reverse chaining, among the temporally partitioned storage structures, was incorporated in the prototype to enhance its performance.