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Simulating MDBS Transaction Management Protocols

Simulating MDBS Transaction Management Protocols. Researchers: Ramon Lawrence, Aruna Adil, Ken Barker University of Manitoba. TR Labs - Winnipeg. Motivations and Goals. Motivations: tackle the interoperability problem of database systems

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Simulating MDBS Transaction Management Protocols

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

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

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

  4. Global Transactions GTM subtransactions GTS GTS GTS GTS LDBS LDBS LDBS LDBS Local Transactions 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

  5. MDBS Simulation Overview • A MDBS is simulated by combining several local database simulators into a logical entity. • Each local database simulator: • simulates a relational strict-2PL database • the relational model is common in industry and is used in products by Oracle, Sybase, and IBM • models database structure, transaction frequency, and database management protocols • Global queries presented to the MDBS are divided into queries for the local databases. • The protocol that insures the information is correct in all local databases is called a global transaction management (GTM) protocol. • Two different GTM protocols were simulated on a MDBS configuration to determine their relative performance.

  6. The Ticket GTM Simulation Results • The Ticket GTM protocol uses tickets at each local database to detect conflicts and insure the data is consistent. • optimistic algorithm • has the potential for high concurrency and performance • Simulation results: • algorithm creates too many conflicts between global transactions which causes global deadlocks, global transaction aborts, and local database overloading. • Thus, the Ticket GTM protocol would not be a good protocol to use in a production environment.

  7. The GSS GTM Simulation Results • The Global Serial Scheduler (GSS) GTM protocol schedules some subtransactions of global transactions serially to prevent conflicts at local databases. • This method prevents conflicts while the ticket method detected conflicts after they occurred. • The GSS is a pessimistic algorithm • Simulation results show that the GSS algorithm has good performance despite some serial executions because it: • has no possibility for global deadlock or abort • executes transactions in the order they are submitted • Thus, the GSS algorithm may be a better choice in a production environment.

  8. Conclusions and Future Work • Conclusions: • Defining protocols for efficiently combining existing databases systems into a MDBS is difficult because of performance concerns. • Simulating a MDBS with different protocols will provide insight into the performance of the protocols and any possible improvements. • Current protocols are inadequate for use in wide-scale. production multidatabase systems. • Future Work: • allowing object-oriented local databases • simulating other GTM protocols and MDBS configurations • designing new, more efficient GTM protocols

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

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