Simulating MDBS Transaction Management Protocols TRLabs - Winnipeg Researchers: Ramon Lawrence, Aruna Adil, Ken Barker University of Manitoba Researchers: Ramon Lawrence, Aruna Adil, Ken Barker University of Manitoba

Motivations and Goals è Motivations: u tackle the interoperability problem of database systems u design transaction management protocols that allow legacy database systems to be integrated smoothly u examine problems with current protocols and determine ways to improve their performance u model how a multidatabase system (MDBS) behaves under different load conditions and configurations è Goals: u create a MDBS simulator capable of handling different configurations, load conditions, and protocols u simulate current protocols to determine their performance u design new protocols based on simulation results

Database Terminology è database system - a database and a system to manage the data è transaction - an atomic sequence of operations applied to the database è global transaction - a transaction spanning more than one database è transaction management - a protocol for mediating access to database data è multidatabase system (MDBS) - a collection of autonomous, local databases participating in a global database system to share data

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

MDBS Simulation 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 ïthe relational model is common in industry and is used in products by Oracle, Sybase, and IBM u models database structure, transaction frequency, and database management protocols è Global queries presented to the MDBS are divided into queries for the local databases. è The protocol that insures the information is correct in all local databases is called a global transaction management (GTM) protocol. è Two different GTM protocols were simulated on a MDBS configuration to determine their relative performance.

The Ticket GTM Simulation Results è The Ticket GTM protocol uses tickets at each local database to detect conflicts and insure the data is consistent. u optimistic algorithm u has 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.

The GSS GTM Simulation Results è The Global Serial Scheduler (GSS) GTM protocol schedules some subtransactions of global transactions serially to prevent conflicts at local databases. è This method prevents conflicts while the ticket method detected conflicts after they occurred. u The GSS is a pessimistic algorithm è Simulation results show that the GSS algorithm 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 may be a better choice in a production environment.

Conclusions and Future Work è Conclusions: u Defining protocols for efficiently combining existing databases systems into a MDBS is difficult because of performance concerns. u Simulating a MDBS with different protocols will provide insight into the performance of the protocols and any possible improvements. u Current protocols are inadequate for use in wide-scale. 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

Industrial Applications è Multidatabase systems are useful in industry because: u many corporations have different database management systems which could be integrated into one system u database systems may be combined when a corporation acquires new companies or changes its organization u interoperation of databases on the Internet è Multidatabase systems (MDBSs) are not prevalent in industry because: u it is difficult to integrate different database schemas u current MDBS transaction protocols are inefficient è Simulating a MDBS allows for: u better understanding of MDBS limitations u modeling of a specific MDBS configuration u designing/comparing protocols to more efficiently manage a MDBS system