simulating mdbs transaction management protocols

Simulating MDBS Transaction Management ProtocolsRamon Lawrence, Ken Barker, Aruna Adil

Simulating MDBS Transaction Simulating MDBS Transaction Management ProtocolsManagement Protocols

Simulating MDBS Transaction Simulating MDBS Transaction Management ProtocolsManagement Protocols

Ramon Lawrence, Ken Barker, Aruna AdilRamon Lawrence, Ken Barker, Aruna AdilDepartment of Computer ScienceDepartment of Computer ScienceUniversity of Manitoba, CanadaUniversity of Manitoba, Canada

{umlawren, barker}@cs.umanitoba.ca{umlawren, barker}@cs.umanitoba.ca

Ramon Lawrence, Ken Barker, Aruna AdilRamon Lawrence, Ken Barker, Aruna AdilDepartment of Computer ScienceDepartment of Computer ScienceUniversity of Manitoba, CanadaUniversity of Manitoba, Canada

{umlawren, barker}@cs.umanitoba.ca{umlawren, barker}@cs.umanitoba.ca


Outline

Introduction The MDBS architecture and the transaction

management problem Previous work Simulation architecture

LDBS simulation MDBS simulation

Simulation results and comparisons Future work and conclusions


Database Terminology

transaction management - a protocol for mediating access to database data

global transaction - a transaction spanning more than one database

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 GTS GTSGTS

Local Transactions

LDBS LDBS LDBS LDBS

subtransactions


The Transaction Management Problem

Transaction management (TM) is the process of ensuring data access results in correct and consistent data

TM is harder in a MDBS because: the global-level TM has no control over how

LDBSs store and access data databases are distributed so network

delays affect query performance must handle different database models and

systems data may be incomplete or inconsistent

between databases


Previous Work

There has been several algorithms proposed for TM in a MDBS including:

Ticket serializability (Georgakopoulos) Database serializability (Barker) others …

The major problems with these algorithms is that they are too inefficient to be implemented in a real system.


Motivations and Goals

Motivations: No simulation system capable of comparing

current and proposed protocols has been implemented

Examine problems with current protocols and determine ways to improve their performance

Goals: create a MDBS simulator capable of handling

different configurations, load conditions, and protocols

simulate current protocols to determine their performance and design new protocols based on simulation results


MDBS Simulator 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

used in products by Oracle, Sybase, and IBM

models database structure, transaction frequency, and database management protocols

processes transactions originating from local and global queries


MDBS Simulator Overview (cont.)

At the global level, the global transaction manager:

processes global transactions and sends queries to the LDBSs

enforces global-level consistency compiles statistics on transaction

residence times and number of aborts


Using the MDBS Simulator

The MDBS simulator was used to compare two GTM protocols:

Ticket method protocol Global Serial Scheduler (GSS)

Each protocol was simulated on the identical MDBS configuration with identical transaction loads at both the local and global levels


The Ticket GTM Simulation Results

The Ticket GTM protocol uses tickets at each database to detect conflicts and insure the data is consistent

optimistic algorithm with 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.


The GSS GTM Simulation Results

The Global Serial Scheduler (GSS) schedules some transactions serially to prevent conflicts at local databases

prevents conflicts (pessimistic algorithm)

Results show that it 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 is a better choice in a production environment.


MDBS Simulation Results

GT Residence Time vs. Interarrival Time

0

20

40

60

80

100

120

140

160

100 80 50 35 25 20 15 10 5 2 1

GT Interarrival Time (sec.)

GT

Re

sid

en

ce

Tim

e (

se

c.)

Ticket Method (res.time) GSS (res. time)


MDBS Simulation Results (cont.)

Transaction Residence Times at LDBS1

0

0.5

1

1.5

2

2.5

3

3.5

100 80 50 35 25 20 15 10 5 2 1

GT Interarrival Time (sec.)

Re

sid

en

ce

Tim

e (

sec

.)

GSS Ticket Method


MDBS Simulation Results (cont.)

GT Arrival Rate vs. Number of Global Aborts

0

10

20

30

40

50

60

70

80

90

100

0 0.02 0.04 0.06 0.08 0.1 0.12

GT Arrival Rate

# o

f a

bo

rts

Ticket Method


Conclusions and Future Work

Conclusions: Defining GTM protocols is difficult because of

performance concerns Simulating a MDBS provides insight into the

protocols and possible improvements Current protocols are inadequate for use in

production multidatabase systems

Future Work: allowing object-oriented local databases simulating other GTM protocols and MDBS

configurations designing new, more efficient GTM protocols

simulating mdbs transaction management protocols

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