1. J2EE Lecture 12: Transaction
Dr. Ming Qiu
Xiamen University
Software School

2. Mastering EJB 3.0, Chap 10
12.1 Introduction
Transactions make the mission-critical operations run predictably
In the past, developers need to code directly to a transaction API.
With EJB, you can gain the benefits of transactions without writing any transaction code

3. 12.2 Motivation for transactions
Mastering EJB 3.0, Chap 10
12.2 Motivation for transactions
Atomic operations
Transfer funds from one account to another

4. 12.2 Motivation for transactions
Mastering EJB 3.0, Chap 10
12.2 Motivation for transactions
Many problems with this approach
The code is bulky and unwieldy
Need to consider every possible problem that might occur an consider how to roll back our changes
Error handling gets out of control if we perform more complex processes
Testing this code is a challenge
We would like a way to perform both operations in a single, large, atomic operation

5. 12.2 Motivation for transactions
Mastering EJB 3.0, Chap 10
12.2 Motivation for transactions
Network or Machine Failure

6. 12.2 Motivation for transactions
Mastering EJB 3.0, Chap 10
12.2 Motivation for transactions
Multiple Users Sharing Data

7. 12.3 Benefits of Transactions
Mastering EJB 3.0, Chap 10
12.3 Benefits of Transactions
To avoid all these problems
Use transactions
Transaction
A series of operations that appear to execute as one large, atomic operation
Guarantee an all-or-nothing value proposition
Account for network or machine failure in a graceful, reliable way
Allow multiple users to share the same data
Guarantee that any update of data is completely and wholly written

8. 12.3 Benefits of Transactions
Mastering EJB 3.0, Chap 10
12.3 Benefits of Transactions
EJB in Action, Chap 6
The ACID Properties
Atomicity
Guarantees that many operations are bundled together and appear as one contiguous unit of work
Consistency
Guarantees that a transaction leaves the system’s state to be consistent after a transaction completes.
The system need not be in a consistent state during the transaction
The balance of account may temporarily be negative during the transaction.

9. 12.3 Benefits of Transactions
Mastering EJB 3.0, Chap 10
12.3 Benefits of Transactions
Isolation
Protects concurrently executing transaction without seeing each other’s incomplete results.
Ensures that nobody touches your data while you are in the transaction
Locks on data are automatically assigned as necessary
Durability
Guarantees that updates to managed resource
A transaction, once committed, is guaranteed to become permanent.
Implemented by using transaction logs in the database server

10. Distributed System Concepts and Design, Chap 16
12.4 Transactional Models
Transactions originate from database management systems. In that context, a transaction is an execution of a program that accesses a database.
Transactions were introduced to distributed systems in the form of transactional file servers
a transaction is an execution of a sequence of client requests for file operations.
From the client’s point of view, a transaction is a sequence of operations that forms a single step, transforming the server data from one consistent state to another.

11. 12.4 Transactional Models Flat Transactions
Mastering EJB 3.0, Chap 10
12.4 Transactional Models
Flat Transactions
A series of operations that are performed atomically as a single unit of work
Problems that make a transaction abort
Invalid parameters passed to one of the components
An invariant system state was violated
Hardware or software failure

12. Mastering EJB 3.0, Chap 10
12.4 Transactional Models

13. 12.4 Transactional Models How transactional State is Rolled Back
Mastering EJB 3.0, Chap 10
12.4 Transactional Models
How transactional State is Rolled Back
When Persist operations happen in a transaction,
Resource manager does not permanently apply the updates to database,
but waits until a commit statement has been issued
If the transaction aborts, the data is not persisted at all.

14. 12.4 Transactional Models Famous trip-planning problem
Mastering EJB 3.0, Chap 10
12.4 Transactional Models
Famous trip-planning problem
Purchase a train ticket from Boston to New York
Purchase a plane ticket from New York to London
Purchase a balloon ride ticket from London to Paris
Finds out that there are no outgoing flight from France
If performed under a flat transaction, roll back the entire transaction
But it may be possible to use another way of transportation out of France

15. 12.4 Transactional Models Nest Transaction
Mastering EJB 3.0, Chap 10
12.4 Transactional Models
Nest Transaction
Enable you to embed atomic units of work within other unit of work
It can roll back without forcing the entire transaction to roll back
The large unit can attempt to retry the embedded unit of work

16. Mastering EJB 3.0, Chap 10
12.4 Transactional Models

17. 12.4 Transactional Models Flat Transactions Nested Transactions
Distributed System Concepts and Design, Chap 17
12.4 Transactional Models
Flat Transactions
Nested Transactions
Client X Y Z M N T 1 2 11 P 12 21 22

18. 12.4 Transactional Models Nested Transactions .
Distributed System Concepts and Design, Chap 17
12.4 Transactional Models
Nested Transactions
a.withdraw(10) c .
deposit(10)
b.withdraw(20)
d.deposit(20)
Client A B C T 1 2 3 4 D X Y Z
T =
openTransaction
openSubTransaction
a.withdraw(10);
closeTransaction
b.withdraw(20);
c.deposit(10);
d.deposit(20);

19. Mastering EJB 3.0, Chap 10
12.4 Transactional Models
EJB in Action, Chap 6
Application servers and enterprise resources (DBMS) do most of the heavy lifting in transaction management.
Resource
Persistent storage from which you read or write
Database, a message queue, or other storage
Resource Manager
DBMS, message queue, or other storage
Transactional Object or transactional component
an enterprise bean, a .NET-managed component, a CORBA component
Transaction Manager (the application server)
Responsible for coordinates a transaction over multiple distributed resources

20. EJB in Action, Chap 6
12.4 Transactional Models

21. Distributed System Concepts and Design, Chap 17
12.4 Transactional Models .
BranchZ
BranchX
participant C D
Client
BranchY B A
join T
a.withdraw(4);
c.deposit(4);
b.withdraw(3);
d.deposit(3);
openTransaction
b.withdraw(T, 3);
closeTransaction
T =
Note: the coordinator is in one of the servers, e.g. BranchX

22. 12.5 Distributed Transaction
Mastering EJB 3.0, Chap 10
12.5 Distributed Transaction
Some possible scenarios where distributed transactions are applicable
Multiple application servers coordinating in the same transaction
Update to different databases in the same transaction
Perform a database update and send or receive a JMS message from a message queue in the same transaction
Connect to a legacy system as well as one or more other type of resources in the same transaction
Requires collaboration of one or more types of resource managers across multiple processes to solve a business problem

23. 12.5 Distributed Transaction
Mastering EJB 3.0, Chap 10
12.5 Distributed Transaction
Durability
Guarantees that all resource updates that are committed are made permanent
If multiple resource managers are involved in transaction, it is difficult to implement durability

24. 12.5 Distributed Transaction
Distributed System Concepts and Design, Chap 17
12.5 Distributed Transaction
The Two-Phase Commit Protocol
Designed to allow any participant to abort its part of a transaction.
Due to the requirement for atomicity, if one part of a transaction is aborted, then the whole transaction must be aborted.

25. 12.5 Distributed Transaction
Distributed System Concepts and Design, Chap 17
12.5 Distributed Transaction
Two-Phase Commit Protocol For Flat Transactions
Phase One
The coordinator sends a canCommit? request to each of the participants in the transaction.
When a participant receives a canCommit? request it replies with its vote (Yes or No) to the coordinator.
Before voting Yes, it prepares to commit by saving objects in permanent storage. If the vote is No the participant aborts immediately.

26. 12.5 Distributed Transaction
Distributed System Concepts and Design, Chap 17
12.5 Distributed Transaction
Two-Phase Commit Protocol For Flat Transactions
Phase Two
The coordinator collects the votes (including its own).
If there are no failures and all the votes are Yes the coordinator decides to commit the transaction and sends a doCommit request to each of the participants.
Otherwise the coordinator decides to abort the transaction and sends doAbort requests to all participants that voted Yes.
Participants that voted Yes are waiting for a doCommit or doAbort request from the coordinator.
When a participant receives one of these messages it acts accordingly and in the case of commit, makes a haveCommitted call as confirmation to the coordinator.

27. 12.5 Distributed Transaction
Distributed System Concepts and Design, Chap 17
12.5 Distributed Transaction
Two-Phase Commit Protocol For Flat Transactions
canCommit?
Yes
doCommit
haveCommitted
Coordinator 1 3
(waiting for votes)
committed
done
prepared to commit
step
Participant 2 4
(uncertain)
status

28. 12.5 Distributed Transaction
Mastering EJB 3.0, Chap 10
12.5 Distributed Transaction

29. 12.6 JTS and JTA Object Transaction Service An optional CORBA service
Mastering EJB 3.0, Chap 10
12.6 JTS and JTA
Object Transaction Service
An optional CORBA service
A suite of well-defined interfaces that specify how transactions can run behind the scenes.
CosTransactions
Basic interfaces that transactional objects, resources, resource managers and transaction managers use to interoperate
CosTSPortability
Offer a portable way to perform transactions with many participant

30. 12.6 JTS and JTA Java Transaction Service Java binding to OTS
Mastering EJB 3.0, Chap 10
12.6 JTS and JTA
Java Transaction Service
Java binding to OTS
Only system developers are interesting in working with JTS
We deal with JTS through the Java Transaction API

31. 12.6 JTS and JTA The Java Transaction API
Mastering EJB 3.0, Chap 10
12.6 JTS and JTA
The Java Transaction API
javax.transaction.xa.XAResource
JTA uses it to communicate with X/Open XA-enabled resource manager
javax.transaction.TransactionManager
JTA uses to communicate with the application server
javax.transaction.UserTransaction
Used by beans and other application programs to work with the EJB transactions

32. Mastering EJB 3.0, Chap 10

33. 12.7 EJB Transactions Demarcating transactional boundaries
Mastering EJB 3.0, Chap 10
12.7 EJB Transactions
Demarcating transactional boundaries
Who begin a transaction
Who issues either a commit or abort
When each of these steps occurs
Who demarcate the transactional boundaries in EJB world?
You can demarcate the transactions yourself
Let the container do that for you

34. 12.7 EJB Transactions Three kinds of transactions
Mastering EJB 3.0, Chap 10
12.7 EJB Transactions
Three kinds of transactions
Bean-managed transaction
The bean is responsible for issuing a begin, commit or abort statement for the transaction.
Container-managed transaction
The EJB container performs the transaction management
Client-controlled transaction
Write code to start and end the transaction from the client code outside of your bean

35. Mastering EJB 3.0, Chap 10
12.7 EJB Transactions

36. Mastering EJB 3.0, Chap 10
12.7 EJB Transactions

37. Mastering EJB 3.0, Chap 10
12.7 EJB Transactions

38. 12.7 EJB Transactions Choosing a Transaction Style
Mastering EJB 3.0, Chap 10
12.7 EJB Transactions
Choosing a Transaction Style
Bean-managed transaction
You have full control over transactional boundaries
Contained-managed transaction
Simple
Client-managed transaction
use sparingly

39. 12.8 Contained-Managed Transaction
Mastering EJB 3.0, Chap 10
12.8 Contained-Managed Transaction
Do not need to write any code about transaction
Need to provide instructions to container for how to operate transaction
Transaction Attribute Value
In the bean’s deployment descriptor
For all business methods in the bean

40. 12.8 Contained-Managed Transaction
Mastering EJB 3.0, Chap 10
12.8 Contained-Managed Transaction
Contained-Managed Transaction Example

41. 12.8 Contained-Managed Transaction
Mastering EJB 3.0, Chap 10
12.8 Contained-Managed Transaction

42. 12.8 Contained-Managed Transaction
Mastering EJB 3.0, Chap 10
12.8 Contained-Managed Transaction
EJB Transaction Attribute Values
Required
Bean always run in a transaction
Enable bean to start a new transaction or join existing ones
Examples – Charging a credit card
Customer 1 : Customer Service Center
Customer 2: Billing component as part of a purchasing workflow

43. 12.8 Contained-Managed Transaction
Mastering EJB 3.0, Chap 10
12.8 Contained-Managed Transaction
RequiresNew
Always require a new transaction
Suspend the existing transaction
Supports
Make the bean join a existing transaction
Similar to Required
But not start a new transaction
Mandatory
Mandates that a transaction must be already running when the bean method is called.
Throw javax.ejb.EJBTransactionRequiredException, when no transaction is running

44. 12.8 Contained-Managed Transaction
Mastering EJB 3.0, Chap 10
12.8 Contained-Managed Transaction
NotSupported
Do not involve a bean in a transaction at all.
Examples
A calls B, and A begins a transaction
When it come to B, the transaction A started is suspended, and none of B’s operations are transactional
When B completes, A’s transaction is resume
Never
Can not involve a bean in a transaction
Throw javax.ejb.EJBException when involved in a transaction

45. 12.8 Contained-Managed Transaction
Mastering EJB 3.0, Chap 10
12.8 Contained-Managed Transaction

46. 12.8 Contained-Managed Transaction
Mastering EJB 3.0, Chap 10
12.8 Contained-Managed Transaction

47. 12.8 Contained-Managed Transaction
Mastering EJB 3.0, Chap 10
12.8 Contained-Managed Transaction
Contained-Managed Transaction Example

48. 12.8 Contained-Managed Transaction
Mastering EJB 3.0, Chap 10
12.8 Contained-Managed Transaction

49. 12.8 Contained-Managed Transaction
EJB in Action, Chap 6
12.8 Contained-Managed Transaction
Marking a CMT for rollback
The setRollbackOnly and getRollbackOnly methods can only be invoked in an EJB using CMT with these transaction attributes: REQUIRED, REQUIRES_NEW, or MANDATORY.
Otherwise, the container will throw an IllegalStateException.

50. 12.8 Contained-Managed Transaction
EJB in Action, Chap 6
12.8 Contained-Managed Transaction

51. 12.8 Contained-Managed Transaction
EJB in Action, Chap 6
12.8 Contained-Managed Transaction

52. 12.8 Contained-Managed Transaction
EJB in Action, Chap 6
12.8 Contained-Managed Transaction

53. 12.8 Contained-Managed Transaction
Mastering EJB 3.0, Chap 10
12.8 Contained-Managed Transaction

54. 12.8 Contained-Managed Transaction
Mastering EJB 3.0, Chap 10
12.8 Contained-Managed Transaction

55. 12.9 Bean-Managed Transaction
Mastering EJB 3.0, Chap 10
12.9 Bean-Managed Transaction
Demarcate transaction by yourself
Allow for more transaction control than container-managed transactions do
Use the JTA interface
javax.transaction.UserTransaction

56. 12.9 Bean-Managed Transaction
Mastering EJB 3.0, Chap 10
12.9 Bean-Managed Transaction
javax.transaction.UserTransaction

57. 12.9 Bean-Managed Transaction
Mastering EJB 3.0, Chap 10
12.9 Bean-Managed Transaction

58. Mastering EJB 3.0, Chap 10

59. 12.9 Bean-Managed Transaction
Mastering EJB 3.0, Chap 10
12.9 Bean-Managed Transaction
Bean-Managed Transaction Example

60. 12.9 Bean-Managed Transaction
Mastering EJB 3.0, Chap 10
12.9 Bean-Managed Transaction
Complete your transactions in the same method!

61. 12.9 Bean-Managed Transaction
EJB in Action, Chap 6
12.9 Bean-Managed Transaction

62. 12.10 Client-Controlled Transaction
Mastering EJB 3.0, Chap 10
12.10 Client-Controlled Transaction
Use JTA to Control transactions from client code
Get hold of JTA UserTransaction interface
By using resource injection (in a EJB)
By looking it up in the JNDI registry

63. 12.11 Transaction in Spring Spring’s Transaction Manager
Spring in Action, Chap 5
12.11 Transaction in Spring
Spring’s Transaction Manager

64. 12.11 Transaction in Spring HibernateTransactionManager
Spring Framework Doc
12.11 Transaction in Spring
HibernateTransactionManager

65. Spring Framework Doc
12.11 Transaction in Spring

66. Spring Framework Doc
12.11 Transaction in Spring

67. Spring Framework Doc
12.11 Transaction in Spring

68. 12.11 Transaction in Spring Transaction propagation
Spring Framework Doc
12.11 Transaction in Spring
Transaction propagation

69. 12.11 Transaction in Spring Transaction propagation
Spring Framework Doc
12.11 Transaction in Spring
Transaction propagation

70. 12.12 Transaction Isolation
Mastering EJB 3.0, Chap 10
12.12 Transaction Isolation
Isolation Level
READ UNCOMMITTED
Does not offer any isolation guarantees (Highest performance)
READ COMMITTED
Solves the dirty read problem
REPEATABLE READ
Solves the dirty read and unrepeatable read problem
SERIALIZABLE
Solves the dirty read, unrepeatable read and phantom problem

71. 12.12 Transaction Isolation
Mastering EJB 3.0, Chap 10
12.12 Transaction Isolation
READ UNCOMMITTED
No isolation guarantee
Highest Performance
Dangerous to use in mission-critical systems
Appropriate if an instance of the component will be running only when there are no other concurrent transactions.

72. 12.12 Transaction Isolation
Distributed System Concepts and Design, Chap 17
12.12 Transaction Isolation
Dirty Read
a＝200, b=300
Transaction V :
Transaction W :
a.withdraw(100)
aBranch.branchTotal()
b.deposit(100)
a.withdraw(100);
$100
total = a.getBalance()
$100
total = total+b.getBalance()
$300
total = total+c.getBalance()
b.deposit(100)
$300
The other application reads your update before you committed

73. 12.12 Transaction Isolation
Distributed System Concepts and Design, Chap 17
12.12 Transaction Isolation
Dirty Read

74. 12.12 Transaction Isolation
Mastering EJB 3.0, Chap 10
12.12 Transaction Isolation
READ COMMITTED
Read committed data only
Appropriate if the programs want to generate a report
Not mission critical
Create a snap for the committed data
Slower than READ UNCOMMITTED
Default isolation level for most databases
Oracle or Microsoft SQL Server

75. 12.11 Transaction Isolation
Mastering EJB 3.0, Chap 10
12.11 Transaction Isolation
Unrepeatable Read Problem
a＝100, b=200, c=300
Transaction T :
balance = b.getBalance();
a.withdraw(balance/10); U
b.setBalance(balance*1.1);
c.withdraw(balance/10)
balance = b.getBalance();
$200
$220
a.withdraw(balance/10)
$80
$280
balance = b.getBalance();
balance = b.getBalance();
$220
Guarantee by using transactional locks to lock out other transactions from modifying the data

76. 12.11 Transaction Isolation
Distributed System Concepts and Design, Chap 17
12.11 Transaction Isolation
Lost Update
a＝100, b=200, c=300
Transaction T :
balance = b.getBalance();
b.setBalance(balance*1.1);
a.withdraw(balance/10) U
c.withdraw(balance/10)
balance = b.getBalance();
$200
$220
$80
$280

77. 12.12 Transaction Isolation
Hibernate in Action, Chap 10
12.12 Transaction Isolation
Unrepeatable Read

78. 12.12 Transaction Isolation
Mastering EJB 3.0, Chap 10
12.12 Transaction Isolation
REPEATABLE READ
Whenever you read committed data from a database, you will be able to reread the same data again at a later time.
Appropriate if you need to update one or more data elements in a resource

79. 12.12 Transaction Isolation
Mastering EJB 3.0, Chap 10
12.12 Transaction Isolation
The Phantom Problem
Instance A queries the database using some criteria and retrieves a data set
Instance B inserts new data that would satisfy your query
Instance A perform the query again, the result data set changed.

80. 12.12 Transaction Isolation
Hibernate in Action, Chap 10
12.12 Transaction Isolation
Phantom Read

81. 12.12 Transaction Isolation
Mastering EJB 3.0, Chap 10
12.12 Transaction Isolation
SERIALIZABLE
Guarantees that transactions execute serially with respect to each other.
Used for mission-critical systems

82. 12.12 Transaction Isolation
Mastering EJB 3.0, Chap 10
12.12 Transaction Isolation
Transaction Isolation Summary

83. 12.12 Transaction Isolation
Mastering EJB 3.0, Chap 10
12.12 Transaction Isolation
Isolation and Lock
By acquiring lock, transactions guarantee serializability
But it lead to major performance problems
A dead lock scenario can arise
To improve performance, two types of locks are introduced
Read locks and write locks
Locking exists in many cycles
Databases, version control systems, and Java language
EJB abstract concurrency control away from developers via isolation levels

84. 12.12 Transaction Isolation
Mastering EJB 3.0, Chap 10
12.12 Transaction Isolation
Pessimistic and Optimistic Concurrency Control

85. 12.12 Transaction Isolation
Hibernate in Action, Chap 10
12.12 Transaction Isolation
Choosing an isolation model
First, eliminate the read uncommitted isolation level
Secondly, most applications don’t need serializable isolation
a choice between read committed and repeatable read.
Read lock and write lock
Versioned data

86. 12.12 Transaction Isolation
Hibernate in Action, Chap 10
12.12 Transaction Isolation
Enabling versioning in Hibernate
@Entity
public class Item {
...
@Version
@Column(name = "OBJ_VERSION")
private int version; }