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A Mobile Transaction Model that Capture Both the Data and Movement Behavior

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A Mobile Transaction Model that Capture Both the Data and Movement Behavior Presenter: Yuan Wei Nov. 7, 2002 Overview Problem Statement Background Knowledge Proposed ... – PowerPoint PPT presentation

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Title: A Mobile Transaction Model that Capture Both the Data and Movement Behavior


1
A Mobile Transaction Model that Capture Both the
Data and Movement Behavior
  • Presenter Yuan Wei
  • Nov. 7, 2002

2
Overview
  • Problem Statement
  • Background Knowledge
  • Proposed Solution
  • Comparison
  • Critiques

3
  • Problem Statement

4
DBMS Classification
5
Example Scenario
6
Problem Statement
  • Transaction Processing in Mobile Computing
    Systems
  • Distributed Environment
  • Multiple Database Systems
  • Heterogeneous Databases
  • Mobile Users

7
Why?
  • The state of single transaction spans to multiple
    base stations and databases.
  • The client leaves one base station before a
    transaction finishes
  • The client may need to commit or abort the
    operations or transactions that are not at
    current base station
  • Recovery Problem

8
  • Background Knowledge

9
Transaction ACID Properties
  • Atomicity
  • Either the transaction completes, or nothing
    happens at all.
  • Consistency
  • A transaction must begin in a consistent state
    and leave the system in a consistent state.
  • Isolation
  • Transactions are isolated from concurrent
    schedules.
  • Durability
  • Once committed (completed), the results of a
    transaction are Durable.

10
Common Transaction
11
Common Transaction (cont.)
  • Known database (Typically one)
  • Bounded duration (Compared to long transactions)
  • Few or no interactions with other concurrent
    events
  • ACID properties easy to achieve

12
Multi-Database Transaction
  • Operate on data from several databases (known or
    unknown)
  • Multi-database Directory for discovering relevant
    schemas
  • Databases may NOT know each other
  • Databases are autonomous
  • GDBS coordinates with different databases
  • GDBS keep the original individual database
    intact, so typically there is no no global lock,
    no two-phase lock, no two phase commit.
  • ACID very hard to achieve

13
Nested Transactions
  • A nested transaction is a tree of transactions,
    the sub-trees of which are either nested or flat
    transactions.

14
Open Nested Transaction
  • Objective To improve throughput
  • Idea Give up Isolation property
  • The modification of one sub-transaction will be
    visible to all the transactions
  • Solution Compensation Function
  • The abort operation will change the modification
    back
  • Problems Compensation is not enough

15
Long Transaction
  • Informal Definition The transactions that last
    the same magnitude as the mean time failure of
    the computer system on which they run.
  • Example
  • CAD/CAD transaction, VLSI Layout Transactions
  • Problems
  • Vulnerable to Crash
  • Concurrency Bottleneck

16
Split Transaction
  • Objective
  • Solve the problems of long transactions
  • Idea
  • Divide ongoing transactions into two serializable
    transactions
  • Commit data that will not change
  • Advantage
  • Adaptive recovery, added concurrency and
    Serializable access to resources

17
Split Transaction Prerequisites
  • Assume transaction T splits to A and B and A
    proceeds B

18
  • Proposed Solution

19
Some Terms
A Base Station or Mobile Support Stations is
capable of connecting with a mobile unit and is
equipped with a wireless interface.
A Mobile Unit is a mobile computer which is
capable of connecting to the fixed network via a
wireless link.
20
Some Terms (cont.)
  • Source System
  • A collection of registered systems that offer
    information services to mobile user.
  • Example A distributed database system
  • Data Access Agent (DAA)
  • A program on base stations that provides Mobile
    Unit the access to source systems.
  • Mobile Transaction Manager (MTM)
  • A component of DAA which manages the mobile
    transactions.

21
Solution Overview
22
Kangaroo Transaction Definition
23
Kangaroo Transaction Definition
24
Transaction Processing Modes
  • Compensating Mode
  • One JT fails -gt all JTs undone
  • Users provide compensating functions for
    committed JTs. (Difficult Problem)
  • Atomicity Provided, Isolation Violated (Authors
    Claim)
  • Split Mode
  • One JT failure -gt No more new LT or GT for that
    JT
  • Committed JTs are not affected
  • Neither guarantees KT serializability

25
Transaction Processing
  • Transaction Initialization
  • MTM creates a Kangaroo Transaction and a unique
    KTID
  • BTKT -gt MTM Transaction Log
  • MTM creates first Joey Transaction and a unique
    JTID
  • BTJT -gt MTM Transaction Log
  • JT entry -gt Transaction Status Table
  • Increase Joey Transaction Number

26
Transaction Processing (cont.)
  • Transaction Execution
  • Translate JT operations to global and local
    transactions
  • ST entry -gt transaction table
  • BTST -gt MTM Log
  • Send native transaction to DBMS or GDBS

27
Transaction Processing (cont.)
  • Handoff Process
  • At Original Base Station
  • Original DAA starts split operation (Problem?
    Possibility? How does it know?)
  • HOKT -gt Log
  • Flash Log to Disk (Checkpoint)
  • At Destination Base Station
  • CTKT -gt Log
  • KT entry -gt Transaction Status Table

28
Transaction Processing (cont.)
  • Transaction Commit
  • A sub-transaction commits
  • ETST -gt Log
  • If compensating mode -gt Update ST List
  • If split mode -gt Delete ST entry
  • If no active ST for a JT, commit JT
  • ETJT -gt Log
  • Update Transaction Status Table
  • User specifies the end of KT, change KT to
    Committing
  • If no active JT, commit KT
  • ETKT -gt Log

29
Transaction Processing (cont.)
  • Transaction Abort
  • A doubly linked list is maintained between base
    stations by transaction log. User provide head of
    the linked list.
  • Go forward the linked list to restart interrupted
    transaction. Go backward along the linked list to
    abort or compensate JTs.
  • What causes JT abort? LT and GT abort? KT abort?
    Whats the relation between JT and LT, GT?

30
  • Comparison

31
Other Solutions? (Discussion)
  • How about storing transaction information on MU?
  • What needs to be stored in MU.
  • Transaction ID
  • What else is needed?
  • A GDBS service
  • Whats the advantage compare to KT?
  • Management Complexity? Deployment Complexity?
    Scalability?
  • Solve the handoff problems.

32
Critique
  • Too Complex to use
  • Where is GDBS service? How does it work?
  • Leave a lot of complexity to GDBS
  • Desired transaction property not guaranteed
  • Handoff Process (the core process) has problem
  • Split Transaction prerequisites not guaranteed
  • Handoff Time not Determined

33
References
  • 1 Dunham, M. H., Helal, A., Balakrishnan, S. A
    mobile transaction model that captures both the
    data and movement behavior, ACM/Baltzer Journal
    on Special Topics in Mobile Networks and
    Applications (MONET), vol. 2, pp. 149-162, 1997
  • 2 Pu, C., Kaiser, G., Hutchinson, N.
    Split-Transactions For Open-Ended Activities, in
    International Conference on Very Large Databases,
    pp. 26-37, September 1988
  • 3 Y. Breitbart, H. Garcia-Molina, and A.
    Silberschatz. Overview of multidatabase
    transaction management. VLDB Journal,
    1(2)181-240, Oct. 1992.
  • 4http//research.microsoft.com/gray/WICS_99_TP/
    04_TransactionModels.ppt

34
  • Comments and Questions?

Thank You!
35
  • Appendix

36
Local and Global Transaction
37
Kangaroo Transaction
38
Abbreviations
  • GDBS Global Database System
  • BTKT Begin Kangaroo Transaction
  • HOKT Handoff Kangaroo Transaction
  • CTKT Continuing Kangaroo Transaction
  • BTJT Begin Joey Transaction
  • ETJT Commit (End) Joey Transaction
  • BTST Begin Sub-Transaction
  • ETST End Sub-Transaction
  • KTID Kangaroo Transaction ID
  • JTID Joey Transaction ID
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