Concurrent maintenance of views using multiple versions

Materialized views in data warehouses are maintained incrementally, for reasons of efficiency, to present the latest updates to the users. These views are used by many warehouse readers (users) to execute OLAP queries by running several reader sessions and these views are maintained periodically by maintenance transactions. Therefore, there is an inherent problem of maintaining these views while the reader sessions continue to receive consistent data from these views. In this paper, we discuss a method that allows warehouse maintenance transactions to run concurrently with the reader sessions. Concurrency allows the readers to read the data from the views while the maintenance transaction updates these views. In our proposed method we create additional versions of views dynamically that contain only the modified tuples of the views and provide a mechanism to collapse these versions into the views periodically when there are no reader sessions accessing the views. These versions allow the reader sessions to access the old and the new information. The collapsing of the views is done by a low-priority process executing periodically