1. Page 1 Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil Department of Computer Science University of Manitoba, Canada {umlawren, barker}@cs.umanitoba.ca Ramon Lawrence, Ken Barker, Aruna Adil Department of Computer Science University of Manitoba, Canada {umlawren, barker}@cs.umanitoba.ca

2. Page 2 Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil Outline è Introduction è The MDBS architecture and the transaction management problem è Previous work è Simulation architecture u LDBS simulation u MDBS simulation è Simulation results and comparisons è Future work and conclusions

3. Page 3 Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil Database Terminology è transaction management - a protocol for mediating access to database data è global transaction - a transaction spanning more than one database è multidatabase system (MDBS) - a collection of autonomous, local databases participating in a global database system to share data

4. Page 4 Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil MDBS Architecture Global Transaction Manager (GTM) processes global transactions insures information in all LDBSs is consistent submits subtransactions to the GTSs for each LDBS Global Transaction Servers (GTSs) one for each LDBS converts subtransactions from the GTM into a form usable by the LDBS and vice versa Local Database Systems (LDBSs) databases combined into MDBS not changed in MDBS as still process local transactions GTM Global Transactions GTS Local Transactions LDBS subtransactions

5. Page 5 Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil The Transaction Management Problem è Transaction management (TM) is the process of ensuring data access results in correct and consistent data è TM is harder in a MDBS because: u the global-level TM has no control over how LDBSs store and access data u databases are distributed so network delays affect query performance u must handle different database models and systems u data may be incomplete or inconsistent between databases

6. Page 6 Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil Previous Work è There has been several algorithms proposed for TM in a MDBS including: u Ticket serializability (Georgakopoulos) u Database serializability (Barker) u others … è The major problems with these algorithms is that they are too inefficient to be implemented in a real system.

7. Page 7 Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil Motivations and Goals è Motivations: u No simulation system capable of comparing current and proposed protocols has been implemented u Examine problems with current protocols and determine ways to improve their performance è Goals: u create a MDBS simulator capable of handling different configurations, load conditions, and protocols u simulate current protocols to determine their performance and design new protocols based on simulation results

8. Page 8 Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil MDBS Simulator Overview è A MDBS is simulated by combining several local database simulators into a logical entity. è Each local database simulator: u simulates a relational strict-2PL database ïused in products by Oracle, Sybase, and IBM u models database structure, transaction frequency, and database management protocols u processes transactions originating from local and global queries

9. Page 9 Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil MDBS Simulator Overview (cont.) è At the global level, the global transaction manager: u processes global transactions and sends queries to the LDBSs u enforces global-level consistency u compiles statistics on transaction residence times and number of aborts

10. Page 10 Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil Using the MDBS Simulator è The MDBS simulator was used to compare two GTM protocols: u Ticket method protocol u Global Serial Scheduler (GSS) è Each protocol was simulated on the identical MDBS configuration with identical transaction loads at both the local and global levels

11. Page 11 Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil The Ticket GTM Simulation Results è The Ticket GTM protocol uses tickets at each database to detect conflicts and insure the data is consistent u optimistic algorithm with the potential for high concurrency and performance è Simulation results: u algorithm creates too many conflicts between global transactions which causes global deadlocks, global transaction aborts, and local database overloading. è Thus, the Ticket GTM protocol would not be a good protocol to use in a production environment.

12. Page 12 Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil The GSS GTM Simulation Results è The Global Serial Scheduler (GSS) schedules some transactions serially to prevent conflicts at local databases u prevents conflicts (pessimistic algorithm) è Results show that it has good performance despite some serial executions because it: u has no possibility for global deadlock or abort u executes transactions in the order they are submitted è Thus, the GSS algorithm is a better choice in a production environment.

13. Page 13 Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil MDBS Simulation Results

14. Page 14 Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil MDBS Simulation Results (cont.)

15. Page 15 Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil MDBS Simulation Results (cont.)

16. Page 16 Simulating MDBS Transaction Management Protocols Ramon Lawrence, Ken Barker, Aruna Adil Conclusions and Future Work è Conclusions: u Defining GTM protocols is difficult because of performance concerns u Simulating a MDBS provides insight into the protocols and possible improvements u Current protocols are inadequate for use in production multidatabase systems è Future Work: u allowing object-oriented local databases u simulating other GTM protocols and MDBS configurations u designing new, more efficient GTM protocols