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Listing 515 shows a service, , which exposes two service , is not transactional It operations The rst service operation, reads from the database and returns the result The is used to indicate that it does not require , is transactional and is marked a transaction The second operation, It as such with the operational behavior and , and each updates the calls two internal methods, The operation implicitly marks the database through attribute transaction as complete with the nor throws an error, the change from both are If neither marked as complete service uses the internal class for all database The access Note that its constructor opens a connection to the database When goes out of scope and there are no outstanding requests or transactions active, the garbage collector will close the connection Aggressively attempting to close the connection in a destructor will cause an error because a transaction may still be active when the class goes out of scope
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Listing 515 Transactional Operation
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Implementing Transactions (Operation Behavior)
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Listing 515 continued
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The client code for this example is shown in Listing 516 The client is unaware of the transaction on the service
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Implementing Transactions (Operation Behavior)
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Listing 516 Client Calling a Transactional Service
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Because the two internal methods, and , each create a class, they each open separate connections to the database new opens the rst connection in the transaction, the transaction When is part of a local transaction but not a distributed one When it opens the second connection, the transaction is escalated to a distributed transaction so the work can be coordinated across both connections The method prints out the and the of executes withthe transaction, as shown in Figure 510 Notice that out a distributed transaction, because it is the only connection open in the executes, it creates a distribtransaction at that time But when the uted transaction since it is the second connection open with the transaction scope Escalation happens automatically and has a dramatic negative effect on performance Listing 517 shows the optimized code, where the transfer operation and passes that connection to both opens a connection through and so that only one connection is used
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Figure 510 Output from transactional service showing local and distributed transaction IDs
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Listing 517 Transactional Operation Optimized to Avoid Distributed Transactions
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Figure 511 shows the output from the optimized service Notice that the distributed transaction ID stays as all 0s, indicating that no distributed transaction is present
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Figure 511 Output from optimized transactional service
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Flowing Transactions Across Operations When working with distributed systems, transactions sometimes must span service boundaries For instance, if one service managed customer information and another service managed orders, and a user wanted to place an order and ship the product to a new address, the system would need to invoke operations on each service If the transaction completed, the user would expect that both systems were properly updated If infrastructure supports an atomic transactional protocol, the services can be composed into an aggregate transaction as just described WS-AT (Web Service Atomic Transactions) provides the infrastructure for sharing information among participating services to implement the two-phase commit semantics necessary for ACID transactions In WCF, owing transactional information across service boundaries is referred to as transaction ow To ow transactional semantics across service boundaries, the following ve steps must be taken:
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Service contracts must require sessions because this is how information will be shared between the coordinator (typically the client) and the participating services
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Operation behavior must require a transaction scope This will create a new transaction if one is not already present Operation contracts must allow transaction information to ow in the header of messages The binding must enable transaction ow so that the channel can put transaction information into the SOAP header Also note that the binding must supdoes but port sessions because does not The party that initiates the transaction, typically the client, must use a transaction scope when calling the to service operations It must also call commit the changes
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