João Lourenço
Changing the world, one student at a time…
Computer Science Department, NOVA School of Science and Technology, NOVA University Lisbon, Quinta da Torre, P-2829-516 CAPARICA, Portugal — joao.lourenco [AT] fct [DOT] unl [DOT] pt (email)
Ricardo J. Dias (2008)
MSc Student
in
MSc dissertation: Cooperative memory and database transactions 
Period: October 2007 — October 2008
Grade: 17/20
Papers: Euro-Par 2009 (DOI), ComSIS 5:(2)'08 (DOI)
Abstract: Since the introduction of Software Transactional Memory (STM), this topic has received a strong interest by the scientific community, as it has the potential of greatly facilitating concurrent programming by hiding many of the concurrency issues under the transactional layer, being in this way a potential alternative to the lock based constructs, such as mutexes and semaphores. The current practice of STM is based on keeping track of changes made to the memory and, if needed, restoring previous states in case of transaction rollbacks. The operations in a program that can be reversible,by restoring the memory state, are called transactional operations. The way that this reversibility necessary to transactional operations is achieved is implementation dependent on the STM libraries being used. Operations that cannot be reversed,such as I/O to external data repositories (e.g., disks) or to the console, are called non-transactional operations. Non-transactional operations are usually disallowed inside a memory transaction, because if the transaction aborts their effects cannot be undone. In transactional databases, operations like inserting, removing or transforming data in the database can be undone if executed in the context of a transaction. Since database I/O operations can be reversed, it should be possible to execute those operations in the context of a memory transaction. To achieve such purpose, a new transactional model unifying memory and database transactions into a single one was defined, implemented, and evaluated. This new transactional model satisfies the properties from both the memory and database transactional models. Programmers can now execute memory and database operations in the same transaction and in case of a transaction rollback, the transaction effects in both the memory and the database are reverted.