In-depth presentation about Transactions in WCF

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27 April, 2009 WCF Transactions
by Tom Pester

2. 27 April, 2009
WCF Transactions, by Tom Pester2
ACID
Transactions must have the ACID properties.
ACID stands for:
o Atomic
o Consistent
o Isolated
o Durable

3. 27 April, 2009
WCF Transactions, by Tom Pester3
Two-phase commit protocol
Phase 1
The coordinator asks each resource manager to prepare to commit.
Each resource manager responds (votes) to commit or abort the
transaction.
The coordinator collects all votes and makes a decision to commit or
abort the entire transaction.

4. 27 April, 2009
WCF Transactions, by Tom Pester4
Two-phase commit protocol
Phase 2
The coordinator asks each resource manager to commit or abort
based on this decision.
If the resource manager is asked to commit, it acknowledges
completion of the activity. If asked to abort, it rolls back the activity.
The coordinator waits for acknowledgment from all resource
managers that the transaction was successfully committed.

5. 27 April, 2009
WCF Transactions, by Tom Pester5
TransactionScope
using (TransactionScope scope = new TransactionScope( ))
{
Operation1( );
Operation2( );
scope.Complete( );
}

6. 27 April, 2009
WCF Transactions, by Tom Pester6
Lightweight Transaction Manager
 Any number of volatile resource managers
can be enlisted.
 Only a single durable resource manager can
be enlisted.
 No application domain or process boundaries
can be crossed.

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WCF Transactions, by Tom Pester7
Kernel Transaction Manager
 Windows Vista introduced the Kernel
Transaction Manager (KTM) to manage the
resource managers associated with its
Transactional Registry (TxR) and its transaction
filesystem, called Transactional NTFS (TxF).
 When the downstream code within a
TransactionScope enlists one of these
resource managers, the LTM is promoted to
KTM automatically.
o Any number of volatile resource managers can
be enlisted.
o Only a single durable or kernel resource
manager can be enlisted.
o No application domain or process boundaries
can be crossed.

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WCF Transactions, by Tom Pester8
Distributed Transaction Coordinator
o An application, process, or machine boundary is
crossed.
o More than one durable resource manager is
enlisted

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WCF Transactions, by Tom Pester9
WS-AtomicTransaction and WS-Coordination
protocols
 WS-AtomicTransaction (WS-AT) and WS-Coordination (WS-COOR) are
interoperable protocols that enable message-based distributed transactions
over HTTP and across platform boundaries

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WCF Transactions, by Tom Pester10
Enabling WS-AT

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WCF Transactions, by Tom Pester11
Regasm.exe /codebase wsatui.dll

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WCF Transactions, by Tom Pester12
Transactions and System Tiers

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WCF Transactions, by Tom Pester13
Configuring WCF Transactions
Transaction flow between clients and services is a function of
othe binding configuration,
othe service contract requirements
oand the behavior of the service operation being invoked.

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WCF Transactions, by Tom Pester14
Enabling transaction flow
 For a client transaction to flow across a service boundary, the binding must
support transaction flow, which immediately limits you to one of these
standard bindings: NetNamedPipeBinding
oNetTcpBinding
oWSHttpBinding,
oWSDualHttpBinding
oand WSFederationHttpBinding.
<wsHttpBinding>
<binding name="wsHttpTxTransactionFlow="true" />
</wsHttpBinding>

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WCF Transactions, by Tom Pester15
Transaction flow options
The TransactionFlowAttribute
oNotAllowed
oMandatory
oAllowed
[ServiceContract()]
public interface ICountersService
{
[OperationContract]
[TransactionFlow(TransactionFlowOption.Allowed)]
void ResetCounters( );

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WCF Transactions, by Tom Pester16
Service operations and transactions
 Although the TransactionFlowOption does influence the presence of a client
transaction, it does not guarantee that a service operation will use the
transaction.
 In the implementation of a service contract, each operation must opt-in to
support transactions. TransactionScopeRequired property of the
OperationBehaviorAttribute
[OperationBehavior(TransactionScopeRequired=true)]
public void ResetCounters( )
{...}

17. 27 April, 2009
WCF Transactions, by Tom Pester17
TransactionScopeRequired
 When set to false, which is the default setting, the service will never join a
client transaction, nor will it automatically create a new transaction. That
means that if the service code requires a transaction, it would have to do so
manually using a TransactionScope block.
 When set to true, if a client transaction is flowed to the service, the service
operation will join that transaction. If a client transaction is not flowed, a
new transaction is created for the service operation to execute in.

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WCF Transactions, by Tom Pester18
DistributedIdentifier
 An indicator that the service is participating in the client transaction is when
the DistributedIdentifier of the current transaction is set:
 Transaction.Current.TransactionInformation.DistributedIdentifier

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WCF Transactions, by Tom Pester19
TransactionAutoComplete
 Another property of the OperationBehaviorAttribute that affects how
transactions are handled is the TransactionAutoComplete property. By
default, this property is set to true, which means that the consistency bit is
set to true automatically if no exceptions are thrown

[OperationBehavior(TransactionScopeRequired=true,TransactionAutoCompl
ete=false)]

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WCF Transactions, by Tom Pester20
Controlling IsolationLevel
 The System.Transactions namespace defines an IsolationLevel enumeration that defines
the following isolation options
o Chaos
o ReadCommitted
o ReadUncommitted
o RepeatableRead
o Serializable
o Snapshot
o Unspecified
 The last of these settings, Unspecified, is the default.

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WCF Transactions, by Tom Pester21
TransactionOptions
TransactionOptions options = new TransactionOptions( );options.IsolationLevel =
IsolationLevel.Serializable;
using (TransactionScope scope = new
TransactionScope(TransactionScopeOption.Required, options))
{
m_proxy.SetCounter1(int.Parse(this.txtCounter.Text));
m_proxy.SetCounter2(int.Parse(this.txtCounter.Text));
scope.Complete( );
}

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27 April, 2009