Exploiting Versions for On-line Data Warehouse Maintenance in MOLAP Servers

A data warehouse is an integrated database whose data is collected from several data sources, and supports on-line analytical processing (OLAP). Typically, a query to the data warehouse tends to be complex and involves a large volume of data. To keep the data at the warehouse consistent with the source data, changes to the data sources should be propagated to the data warehouse periodically. Because the propagation of the changes (maintenance) is batch processing, it takes long time. Since both query transactions and maintenance transactions are long and involve large volumes of data, traditional concurrency control mechanisms such as two-phase locking are not adequate for a data warehouse environment. We propose a multi-version concurrency control mechanism suited for data warehouses which use multi-dimensional OLAP (MOLAP) servers. We call the mechanism multiversion concurrency control for data warehouses (MVCCDW). To our knowledge, our work is the first attempt to exploit versions for online data warehouse maintenance in a MOLAP environment. MVCC-DW guarantees the serializability of concurrent transactions. Transactions running under the mechanism do not block each other and do not need to place locks. Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the VLDB copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Very Large Data Base Endowment. To copy otherwise, or to republish, requires a fee and/or special permission from the Endowment. Proceedings of the 28th VLDB Conference, Hong Kong, China, 2002