Transactional Services Ricardo Jiménez-Peris Marta Patiño-Martínez Technical University of Madrid 1 st Adapt Workshop 23 rd -24 th September 2002 Madrid, Spain

23-24 Sept st Adapt Workshop, Madrid 2 Talk Outline Work on transactional systems: –Previous work. –Current work. –Possible contributions to the project. Resources: –Team. –Computing resources. –Funding.

23-24 Sept st Adapt Workshop, Madrid 3 Previous and current work on transactional systems Our previous work on transactional systems has dealt with different aspects of them including: –Design of an advanced transaction model supporting multithreaded execution of nested transactions and conversational interaction. –Development of an Ada 95 TP monitor implementing the above model. –Replication middleware for databases (joint work at ETHZ with Bettina and Gustavo). –A low latency commit service (joint work with Gustavo). –Deterministic scheduling of replicated multithreaded transactional processes.

23-24 Sept st Adapt Workshop, Madrid 4 Multithreaded Nested Transactions: Previous work The model is an extension of the nested transaction model. Unlike the traditional nested model that only allows competitive concurrency (concurrent subtransactions are isolated among them), it supports cooperative concurrency. This is useful, for instance, to add transactional semantics to a cooperative distributed server or to allow cooperative multithreading within a transaction.

23-24 Sept st Adapt Workshop, Madrid 5 Multithreaded Nested Transactions: Contributions to the project We expect that the knowledge gained in this work will help us in developing an advanced transaction model suitable for transactional workflow part of WP2. The experience with the Acta framework will also help in formalizing the model and formally proving its properties.

23-24 Sept st Adapt Workshop, Madrid 6 TP Monitor: Previous work The novelties of the TP monitor were: –Its flexible architecture that allowed to change the concurrency control and recovery protocols (inspired by Arjuna). –It supported logical logging, therefore enabling advanced concurrency control like Commutative Locking. –It supported the multithreaded nested transaction model. –It had support for replicated and cooperative transactional servers.

23-24 Sept st Adapt Workshop, Madrid 7 TP Monitor: Current work The TP monitor is being reimplemented in Java. Currently, the centralized concurrency control and recovery has been implemented. The distributed part is expected to be finished by Christmas.

23-24 Sept st Adapt Workshop, Madrid 8 TP Monitor: Contributions to the Project This work can be extended to contribute to the project in the following ways: –The resulting transactional engine is very flexible and will (hopefully) be able to support a wide variety of advanced transaction models to be used by WP2-3. –It can be used as a base for an EJB implementation providing nested transactions, if found useful for the project.

23-24 Sept st Adapt Workshop, Madrid 9 Replication Middleware: Previous work The middleware extends previous work from Bettina and Gustavo on database replication (Postgres-R). Their work focused on how to achieve scalable eager database replication within the database (white box approach). Our joint work with them extended this work on how to implement the replication outside the database in a middleware layer with a reasonable efficiency (gray box approach). More details will be given later by Bettina. Recently, we have extended the results on online recovery from Bettina, Alberto and Ozalp to apply them to the replication middleware.

23-24 Sept st Adapt Workshop, Madrid 10 Replication Middleware: Current work Currently, there is a PhD student working on load balancing algorithms within the middleware layer, and a TPC-W implementation to measure the improvement. We are currently implementing the online recovery within the replication middleware. We are currently extending the replication protocols to deal with wide area replication.

23-24 Sept st Adapt Workshop, Madrid 11 Replication Middleware: Contributions to the Project The results from this research will be directly applicable to the BS middleware. Availability, online recovery, and load balancing are essential adaptive properties. The middleware is more or less independent of the underlying data store being replicated. Therefore, in principle, it can be applied (in addition to databases) to object containers such as EJBs.

23-24 Sept st Adapt Workshop, Madrid 12 Commit Service: Previous and Current Work This work reduces the cost (in terms of latency) of non-blocking atomic commitment to two rounds by combining optimistic commit, optimistic delivery of uniform multicast (extending previous work from ETHZ), and replication. We are currently implementing the service in Java.

23-24 Sept st Adapt Workshop, Madrid 13 Commit Service: Contributions to the Project This work can be extended to contribute to the project: –Providing efficient and non-blocking atomic commit for BSs. –Supporting BTP (Business Transaction Protocol) for CSs and providing the necessary infrastructure for transactional web services.

23-24 Sept st Adapt Workshop, Madrid 14 Deterministic Scheduling of Multithreaded Transactional Servers Previous work on active replication restricted servers to be single-threaded to guarantee deterministic behavior. In this work, we extended previous work by enabling the replication of multithreaded transactional servers. Additionally, this work tackles with servers with a conversational interface (similar to stateful session beans). Based on total ordered multicast and a deterministic scheduler that schedules all threads in the same way at all replicas without recurring to inter-replica communication. This work can contribute to the project by enabling replication of stateful session beans and entity beans.

23-24 Sept st Adapt Workshop, Madrid 15 Resources Team: –2 Professors. –2 PhD Students: One already working on load balancing for the middleware layer. –A group of undergraduate students.

23-24 Sept st Adapt Workshop, Madrid 16 Resources Lab: –A 20-site cluster (dual AMD k7) (50% funded by the project). Funding: –A complementary grant has been requested to the Spanish Ministry of Science and Technology to cover the 50% of “equipment”, “travel and subsistence”, and “other specific costs” not funded by EU.