8/14/2019 Distributed Transaction Model

1/17

Distributed TransactionDistributed Transaction

ModelModel

Presented by:-Presented by:-Rohit SrivastavaRohit Srivastava

&&

Ashutosh TripathiAshutosh Tripathi

8/14/2019 Distributed Transaction Model

2/17

DefinitionDefinition

AA distributed transactiondistributed transaction is an operation bundle, in whichis an operation bundle, in whichtwo or more network hosts are involved.two or more network hosts are involved.

Transaction should contain 4 ACID propertiesTransaction should contain 4 ACID properties

1.1. AtomicityAtomicity (ability of BBMS to gurantee that all tasks are(ability of BBMS to gurantee that all tasks areperformed)performed)

2.2. ConsistencyConsistency (DBMS remain in consistent state before(DBMS remain in consistent state beforeand after transaction)and after transaction)

3.3. IsolationIsolation (other operations cannot access data during(other operations cannot access data duringtransaction)transaction)

4.4. DurabilityDurability (once transaction is done then it may remain(once transaction is done then it may remainin persistent state)in persistent state)

8/14/2019 Distributed Transaction Model

3/17

System StructureSystem Structure

TM1

TMn

TCnTC1 TransactionCoordinator

Transaction

Manager

Computer 1 Computer n

8/14/2019 Distributed Transaction Model

4/17

ResponsibiltiesResponsibilties

Transaction Manager:-Transaction Manager:- Managing a log for recovery purposeManaging a log for recovery purpose Participating in an appropriate ConcurrencyParticipating in an appropriate Concurrency

Control to coordinate concurrent executionControl to coordinate concurrent execution

Transaction Coordinator:-Transaction Coordinator:- Starting the execution of transactionStarting the execution of transaction Breaking transaction into subtransactions andBreaking transaction into subtransactions and

distribute them to sites for executiondistribute them to sites for execution Coordinating the termination of transactionCoordinating the termination of transaction

8/14/2019 Distributed Transaction Model

5/17

Commit ProtocolsCommit Protocols

To ensure Atomicity property theTo ensure Atomicity property the

Transaction Cordinator mustTransaction Cordinator must

execute commit protocols. Thereexecute commit protocols. There

are 2 types of Commit Protocols:-are 2 types of Commit Protocols:-

1.1. Two Phase Commit protocolTwo Phase Commit protocol

2.2. Three Phase Commit protocolThree Phase Commit protocol

8/14/2019 Distributed Transaction Model

6/17

Two Phase CommitTwo Phase Commit

It comprises of 3 phases:-It comprises of 3 phases:-

1.1. Prepare PhasePrepare Phase:- The initiating node in the:- The initiating node in thetransaction asks the other participating nodes totransaction asks the other participating nodes topromise to commit or roll back the transaction.promise to commit or roll back the transaction.

2.2. Commit PhaseCommit Phase:- The initiating node asks all:- The initiating node asks allparticipating nodes to commit the transaction. Ifparticipating nodes to commit the transaction. Ifthis outcome is not possible, then all nodes arethis outcome is not possible, then all nodes areasked to roll back.asked to roll back.

3.3. Forget PhaseForget Phase:- The global coordinator forgets:- The global coordinator forgetsabout the transaction.about the transaction.

8/14/2019 Distributed Transaction Model

7/17

Types of Responses in theTypes of Responses in the

Prepare PhasePrepare Phase

PreparedPrepared:- Data on the node has been:- Data on the node has been

modified by a statement in the distributedmodified by a statement in the distributed

transaction, and the node has successfullytransaction, and the node has successfully

prepared.prepared. Read-onlyRead-only:- No data on the node has:- No data on the node has

been, or can be, modified (only queried),been, or can be, modified (only queried),

so no preparation is necessary.so no preparation is necessary.

AbortAbort:- The node cannot successfully:- The node cannot successfully

prepare.prepare.

8/14/2019 Distributed Transaction Model

8/17

Steps in the Prepare PhaseSteps in the Prepare Phase

The node requests that itsThe node requests that its descendantsdescendants, that is, the, that is, thenodes subsequently referenced, prepare to commit.nodes subsequently referenced, prepare to commit.

The node checks to see whether the transactionThe node checks to see whether the transactionchanges data on itself or its descendants. If there is nochanges data on itself or its descendants. If there is no

change to the data, then the node skips the remainingchange to the data, then the node skips the remainingsteps and returns a read-only response.steps and returns a read-only response.

The node allocates the resources it needs to commitThe node allocates the resources it needs to committhe transaction if data is changed.the transaction if data is changed.

8/14/2019 Distributed Transaction Model

9/17

ContCont

The node saves redo records corresponding toThe node saves redo records corresponding tochanges made by the transaction to its onlinechanges made by the transaction to its onlineredo log.redo log.

The node guarantees that locks held for theThe node guarantees that locks held for thetransaction are able to survive a failure.transaction are able to survive a failure.

The node responds to the initiating node with aThe node responds to the initiating node with a

prepared response or, if its attempt or theprepared response or, if its attempt or theattempt of one of its descendents to prepare wasattempt of one of its descendents to prepare wasunsuccessful, with an abort response.unsuccessful, with an abort response.

8/14/2019 Distributed Transaction Model

10/17

Steps in the Commit PhaseSteps in the Commit Phase

The global coordinator instructs theThe global coordinator instructs thecommit point site to commit.commit point site to commit.

The commit point site commits.The commit point site commits.

The commit point site informs the globalThe commit point site informs the globalcoordinator that it has committed.coordinator that it has committed.

The global and local coordinators send aThe global and local coordinators send amessage to all nodes instructing them tomessage to all nodes instructing them tocommit the transaction.commit the transaction.

8/14/2019 Distributed Transaction Model

11/17

ContCont

At each node, Site commits the local portionAt each node, Site commits the local portionof the distributed transaction and releasesof the distributed transaction and releaseslocks.locks.

At each node, Site records an additional redoAt each node, Site records an additional redoentry in the local redo log, indicating thatentry in the local redo log, indicating thatthe transaction has committed.the transaction has committed.

The participating nodes notify the globalThe participating nodes notify the globalcoordinator that they have committed.coordinator that they have committed.

8/14/2019 Distributed Transaction Model

12/17

Steps of Forget PhaseSteps of Forget Phase

After receiving notice from the globalAfter receiving notice from the globalcoordinator that all nodes havecoordinator that all nodes havecommitted, the commit point site erasescommitted, the commit point site erasesstatus information about this transaction.status information about this transaction.

The commit point site informs the globalThe commit point site informs the global

coordinator that it has erased the statuscoordinator that it has erased the statusinformation.information.

The global coordinator erases its ownThe global coordinator erases its owninformation about the transaction.information about the transaction.

8/14/2019 Distributed Transaction Model

13/17

Failures of Two Phase ProtocolFailures of Two Phase Protocol

Failure of a participating siteFailure of a participating site

Failure of a CoordinatorFailure of a Coordinator

Network PartitionNetwork Partition

8/14/2019 Distributed Transaction Model

14/17

Recovery and Concurrency ControlRecovery and Concurrency Control

In doubt transactionsIn doubt transactions

Noting lock informationNoting lock information

Faster RecoveryFaster Recovery

8/14/2019 Distributed Transaction Model

15/17

Three Phase Commit ProtocolThree Phase Commit Protocol

Extension of Two Phase ProtocolExtension of Two Phase Protocol

Select new CoordinatorSelect new Coordinator

Property of Non BlockingProperty of Non Blocking

8/14/2019 Distributed Transaction Model

16/17

RefrencesRefrences

Database System Concepts: Henry F.Database System Concepts: Henry F.

KorthKorth

http://stonesoup.esd.ornl.gov/http://stonesoup.esd.ornl.gov/

http://extremelinux.esd.ornl.gov/http://extremelinux.esd.ornl.gov/

http://www.beowulf.org/http://www.beowulf.org/

http://www.cacr.caltech.edu/researchttp://www.cacr.caltech.edu/research/beowulf/h/beowulf/

http://beowulf-underground.org/http://beowulf-underground.org/

8/14/2019 Distributed Transaction Model

17/17

Thank You