- 1 - Supporting Parallelism in Engineering Databases by Nested Transactions

Non-standard database systems supporting complex engineering applications are prime candidates for the exploitation of inherent parallelism in order to reduce the response time for user requests. Nested transactions are proposed as a control structure to achieve medium or even small grain parallelism. This paper investigates the design concepts and describes an implementation of the transaction management in a multi-layered database system running in a workstation-server environment. The tasks of the transaction management are structured according to the ACID principle: a transaction manager is responsible for the Atomicity property; furthermore it coordinates three components. A consistency manager achieves Consistency preservation thereby allowing for deferred control or maintenance due to transaction nesting. A lock manager enables Isolated execution where our locking protocol is designed for parent/child as well as sibling parallelism in a transaction hierarchy. Finally, a recovery manager takes care of various failures according to our extended failure model and accomplishes Durability of database updates.