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Transactions
Ye Wu
http://www.ise.gmu.edu/~wuye
SWE 645
Component-based Software Development
2006-10-
© Dr. Ye Wu
2
What is a Transaction
-^
A single unit of work that embodies the various individualsteps that comprise a composite exchange.
–^
Atomictiy – A transaction will be treated as a single unit of work
-^
Consistency – Guarantee that the transaction will leave the systemor data in a consistent state.
-^
Isolation – Data that a transaction accesses will not be affected byany changes make by other transactions until the first transactioncompletes
-^
Durability – When a transaction is committed, any changes to datathat is make must be recorded in permanent storage.
2006-10-
© Dr. Ye Wu
3
Flat Transactional Processing
TransactionExecuting
TransactionCommitted TransactionRolled Back
OK
Abort
2006-10-
© Dr. Ye Wu
4
Nested Transactions Processing
TransactionExecuting
TransactionCommitted
OK Abort
Perform One or more Smaller grained Transactions
TransactionRolled Back
2006-10-
© Dr. Ye Wu
5
Transactions and EJB
Programmatic transactions
Declarative transactions (Container managedtransactions)
Client-Initiated Transactions
2006-10-
© Dr. Ye Wu
6
Transaction Attribute – Container
Managed Transactions
-^
Supports Transactions
–^
Supports – specified method will use a transaction if one is alreadyavailable. Otherwise no transaction.
-^
Required – specified method must always run within a transaction
-^
RequiresNew – specified method must always run within its owntransaction
-^
Mandatory – specified method must be invoked within the contextof a pre-existing transaction
-^
Transactions not Supported
–^
NotSupported – the method should not be run within a transaction
-^
Never -
2006-10-
© Dr. Ye Wu
7
Transaction Attribute Usage
Required – when the code needs to change thevalue of some data
Supports – when the code needs to read data froma data source
NotSupported – Communicating with resourcesthat do not support transactional processing
2006-10-
© Dr. Ye Wu
8
Programmatic Transaction
-^
Maintaining transactional state across multiplemethods in a stateful session bean.
-^
Providing transactional behavior for a resourcethat doesn’t provide transactional processing
-^
Java Transaction Service(JTS) – System level
-^
Java Transaction API(JTA) – Application level
2006-10-
© Dr. Ye Wu
13
Isolation Levels
Example
Customer customer =
entityManager.find(Customer.
class
,id);
R1:
System.
out
.println(custom
er.getFirstName() + " "+customer.getLastName());
R2:
entityManager.refresh(cust omer); System.
out
.println(customer.ge
tFirstName() + " "+customer.getLastName());
Customer customer =
entityManager.find(Customer.
class
,id);
W1:
customer.setFirstName(fir stName);
W2:
customer.setLastName(las tName);
AAA BBB
CCC DDD
2006-10-
© Dr. Ye Wu
14
Isolation LevelsREAD UNCOMMITTED
R1:
System.
out
.println(custom
er.getFirstName() + " "+customer.getLastName());
AAA BBB
R2: System.
out
.println(customer.ge
tFirstName() + " "+customer.getLastName());
CCC BBB
W1:
cust.setFirstName(fName);
CCC BBB
W2:
cust.setLastName(lName);
CCC DDD
2006-10-
© Dr. Ye Wu
15
Isolation Levels
READ COMMITTED
R1:
System.
out
.println(custom
er.getFirstName() + " "+customer.getLastName());
AAA BBB
R2: System.
out
.println(customer.ge
tFirstName() + " "+customer.getLastName());
AAA BBB
W1:
cust.setFirstName(fName);
CCC BBB
W2:
cust.setLastName(lName);
CCC DDD
EJB3.0 Default
2006-10-
© Dr. Ye Wu
16
Isolation Levels
READ COMMITTED
R1:
System.
out
.println(custome
r.getFirstName() + " "+customer.getLastName());
AAA BBB
R2: System.
out
.println(customer.ge
tFirstName() + " "+customer.getLastName());
CCC DDD
W1:
cust.setFirstName(fName);
CCC BBB
W2:
cust.setLastName(lName);
CCC DDD
2006-10-
© Dr. Ye Wu
17
Isolation LevelsREAD REPEATABLE
R1:
System.
out
.println(custome
r.getFirstName() + " "+customer.getLastName());
AAA BBB
R2: System.
out
.println(customer.ge
tFirstName() + " "+customer.getLastName());
AAA BBB
W1:
cust.setFirstName(fName);
CCC BBB
W2:
cust.setLastName(lName);
CCC DDD
EJB3.0 READ Lock
2006-10-
© Dr. Ye Wu
18
Isolation Levels
SERIALIZABLE
R1:
System.
out
.println(custom
er.getFirstName() + " "+customer.getLastName());
R2: System.
out
.println(customer.ge
tFirstName() + " "+customer.getLastName());
W1:
cust.setFirstName(fName);
W2:
cust.setLastName(lName);
EJB3.0 WRITE Lock
2006-10-
© Dr. Ye Wu
19
Locking
Optimistic LockingA model takes an optimistic approach to locking the entity.i.e. it assumes there is a good chance that the transaction inwhich changes are made to an entity will be the only onethat actually changes the entity during that interval.
Pessimistic LockingA model that eagerly obtain a lock on the resource beforeoperating on it.
2006-10-
© Dr. Ye Wu
20
Optimistic Locking
@Entitypublic class Customer implements Serializable {
@Versionprivate long version;public long getVersion() {
return version;
}public void setVersion(long version) {
this.version = version;
} }
