Transcript Simulating MDBS Transaction Management Protocols

Simulating MDBS Transaction Management
Protocols
Researchers:
Ramon Lawrence, Aruna Adil, Ken Barker
University of Manitoba
TRLabs - Winnipeg
Motivations and Goals
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Motivations:
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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:
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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
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
MDBS Architecture
Global Transactions
Global Transaction Manager (GTM)
•processes global transactions
•insures information in all LDBSs is
consistent
•submits subtransactions to the
GTSs for each LDBS
GTM
subtransactions
GTS
GTS
LDBS LDBS
GTS
Global Transaction Servers (GTSs)
GTS
•one for each LDBS
•converts subtransactions from the
GTM into a form usable by the
LDBS and vice versa
LDBS LDBS Local Database Systems (LDBSs)
Local Transactions
•databases combined into MDBS
•not changed in MDBS as still
process local transactions
MDBS Simulation Overview
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A MDBS is simulated by combining several local
database simulators into a logical entity.
Each local database simulator:
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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.
The Ticket GTM Simulation Results
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The Ticket GTM protocol uses tickets at each local
database to detect conflicts and insure the data is
consistent.
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Simulation results:
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optimistic algorithm
has the potential for high concurrency and performance
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.
The GSS GTM Simulation Results
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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.
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Simulation results show that the GSS algorithm has
good performance despite some serial executions
because it:
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The GSS is a pessimistic algorithm
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.
Conclusions and Future Work
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Conclusions:
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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:
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allowing object-oriented local databases
simulating other GTM protocols and MDBS
configurations
designing new, more efficient GTM protocols
Industrial Applications
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Multidatabase systems are useful in industry because:
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Multidatabase systems (MDBSs) are not prevalent in
industry because:
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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
it is difficult to integrate different database schemas
current MDBS transaction protocols are inefficient
Simulating a MDBS allows for:
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better understanding of MDBS limitations
modeling of a specific MDBS configuration
designing/comparing protocols to more efficiently
manage a MDBS system