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Supporting Distributed Transactions

SQL Server Native Client OLE DB provider consumers can use the ITransactionJoin::JoinTransaction method to participate in a distributed transaction coordinated by Microsoft Distributed Transaction Coordinator (MS DTC).

MS DTC exposes COM objects that allow clients to initiate and participate in coordinated transactions across multiple connections to a variety of data stores. To initiate a transaction, the SQL Server Native Client OLE DB provider consumer uses the MS DTC ITransactionDispenser interface. The BeginTransaction member of ITransactionDispenser returns a reference on a distributed transaction object. This reference is passed to the SQL Server Native Client OLE DB provider using JoinTransaction.

MS DTC supports asynchronous commit and abort on distributed transactions. For notification on asynchronous transaction status, the consumer implements the ITransactionOutcomeEvents interface and connects the interface to an MS DTC transaction object.

For distributed transactions, the SQL Server Native Client OLE DB provider implements ITransactionJoin::JoinTransaction parameters as follows.

Parameter

Description

punkTransactionCoord

A pointer to an MS DTC transaction object.

IsoLevel

Ignored by the SQL Server Native Client OLE DB provider. The isolation level for MS DTC-coordinated transactions is determined when the consumer acquires a transaction object from MS DTC.

IsoFlags

Must be 0. The SQL Server Native Client OLE DB provider returns XACT_E_NOISORETAIN if any other value is specified by the consumer.

POtherOptions

If not NULL, the SQL Server Native Client OLE DB provider requests the options object from the interface. The SQL Server Native Client OLE DB provider returns XACT_E_NOTIMEOUT if the options object's ulTimeout member is not zero. The SQL Server Native Client OLE DB provider ignores the value of the szDescription member.

This example coordinates transaction by using MS DTC.

// Interfaces used in the example.
IDBCreateSession*       pIDBCreateSession   = NULL;
ITransactionJoin*       pITransactionJoin   = NULL;
IDBCreateCommand*       pIDBCreateCommand   = NULL;
IRowset*                pIRowset            = NULL;

// Transaction dispenser and transaction from MS DTC.
ITransactionDispenser*  pITransactionDispenser = NULL;
ITransaction*           pITransaction       = NULL;

    HRESULT             hr;

// Get the command creation interface for the session.
if (FAILED(hr = pIDBCreateSession->CreateSession(NULL,
     IID_IDBCreateCommand, (IUnknown**) &pIDBCreateCommand)))
    {
    // Process error from session creation. Release any references and
    // return.
    }

// Get a transaction dispenser object from MS DTC and
// start a transaction.
if (FAILED(hr = DtcGetTransactionManager(NULL, NULL,
    IID_ITransactionDispenser, 0, 0, NULL,
    (void**) &pITransactionDispenser)))
    {
    // Process error message from MS DTC, release any references,
    // and then return.
    }
if (FAILED(hr = pITransactionDispenser->BeginTransaction(
    NULL, ISOLATIONLEVEL_READCOMMITTED, ISOFLAG_RETAIN_DONTCARE,
    NULL, &pITransaction)))
    {
    // Process error message from MS DTC, release any references,
    // and then return.
    }

// Join the transaction.
if (FAILED(pIDBCreateCommand->QueryInterface(IID_ITransactionJoin,
    (void**) &pITransactionJoin)))
    {
    // Process failure to get an interface, release any references, and
    // then return.
    }
if (FAILED(pITransactionJoin->JoinTransaction(
    (IUnknown*) pITransaction, 0, 0, NULL)))
    {
    // Process join failure, release any references, and then return.
    }

// Get data into a rowset, then update the data. Functions are not
// illustrated in this example.
if (FAILED(hr = ExecuteCommand(pIDBCreateCommand, &pIRowset)))
    {
    // Release any references and return.
    }

// If rowset data update fails, then terminate the transaction, else
// commit. The example doesn't retain the rowset.
if (FAILED(hr = UpdateDataInRowset(pIRowset, bDelayedUpdate)))
    {
    // Get error from update, then abort.
    pITransaction->Abort(NULL, FALSE, FALSE);
    }
else
    {
    if (FAILED(hr = pITransaction->Commit(FALSE, 0, 0)))
        {
        // Get error from failed commit.
        //
        // If a distributed commit fails, application logic could
        // analyze failure and retry. In this example, terminate. The 
        // consumer must resolve this somehow.
        pITransaction->Abort(NULL, FALSE, FALSE);
        }
    }

if (FAILED(hr))
    {
    // Update of data or commit failed. Release any references and
    // return.
    }

// Un-enlist from the distributed transaction by setting 
// the transaction object pointer to NULL.
if (FAILED(pITransactionJoin->JoinTransaction(
    (IUnknown*) NULL, 0, 0, NULL)))
    {
    // Process failure, and then return.
    }

// Release any references and continue.

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