避免與 FILESTREAM 應用程式中的資料庫作業相衝突

使用 SqlOpenFilestream() 來開啟 Win32 檔案控制代碼以便讀取或寫入 FILESTREAM BLOB 資料的應用程式可能會與在一般交易中管理的 Transact-SQL 陳述式發生衝突錯誤。 這包含需要很長時間才能執行完成的 Transact-SQL 或 MARS 查詢。若要有效避免這些衝突類型，您必須仔細地設計應用程式。

當 SQL Server Database Engine 或應用程式嘗試開啟 FILESTREAM BLOB 時，Database Engine 會檢查相關聯的交易內容。 Database Engine 會根據開啟作業是使用 DDL 陳述式、DML 陳述式、擷取資料或管理交易，來允許或拒絕此要求。下表顯示 Database Engine 根據交易所開啟的檔案類型來判斷允許或拒絕 Transact-SQL 陳述式。

Transact-SQL 陳述式	開啟以便讀取	開啟以便寫入
使用資料庫中繼資料的 DDL 陳述式，例如 CREATE TABLE、CREATE INDEX、DROP TABLE 和 ALTER TABLE。	允許	封鎖並且因逾時而失敗。
使用資料庫所儲存之資料的 DML 陳述式，例如 UPDATE、DELETE 和 INSERT。	允許	拒絕
SELECT	允許	允許
COMMIT TRANSACTION	拒絕*	拒絕*
SAVE TRANSACTION	拒絕*	拒絕*
ROLLBACK	允許*	允許*

* 取消交易，而且交易內容的開啟控制代碼會失效。 應用程式必須關閉所有開啟控制代碼。

範例

下列範例會顯示 Transact-SQL 陳述式和 FILESTREAM Win32 存取如何造成衝突。

A.開啟 FILESTREAM BLOB 進行寫入存取

下列範例會顯示開啟檔案進行唯寫存取的作用。

dstHandle =  OpenSqlFilestream(dstFilePath, Write, 0,
    transactionToken, cbTransactionToken, 0);

//Write some date to the FILESTREAM BLOB.
WriteFile(dstHandle, updateData, …);

//DDL statements will be denied.
//DML statements will be denied.
//SELECT statements will be allowed. The FILESTREAM BLOB is
//returned without the modifications that are made by
//WriteFile(dstHandle, updateData, …).
CloseHandle(dstHandle);

//DDL statements will be allowed.
//DML statements will be allowed.
//SELECT statements will be allowed. The FILESTREAM BLOB
//is returned with the updateData applied.

B.開啟 FILESTREAM BLOB 進行讀取存取

下列範例會顯示開啟檔案進行唯讀存取的作用。

dstHandle =  OpenSqlFilestream(dstFilePath, Read, 0,
    transactionToken, cbTransactionToken, 0);
//DDL statements will be denied.
//DML statements will be allowed. Any changes that are
//made to the FILESTREAM BLOB will not be returned until
//the dstHandle is closed.
//SELECT statements will be allowed.
CloseHandle(dstHandle);

//DDL statements will be allowed.
//DML statements will be allowed.
//SELECT statements will be allowed.

C.開啟並關閉多個 FILESTREAM BLOB 檔案

如果已開啟多個檔案，就會使用限制最嚴格的規則。 下列範例會開啟兩個檔案。 第一個檔案會開啟以便讀取，而第二個檔案會開啟以便寫入。 在開啟第二個檔案之前，系統會拒絕 DML 陳述式。

dstHandle =  OpenSqlFilestream(dstFilePath, Read, 0,
    transactionToken, cbTransactionToken, 0);
//DDL statements will be denied.
//DML statements will be allowed.
//SELECT statements will be allowed.

dstHandle1 =  OpenSqlFilestream(dstFilePath1, Write, 0,
    transactionToken, cbTransactionToken, 0);

//DDL statements will be denied.
//DML statements will be denied.
//SELECT statements will be allowed.

//Close the read handle. The write handle is still open.
CloseHandle(dstHandle);
//DML statements are still denied because the write handle is open.

//DDL statements will be denied.
//DML statements will be denied.
//SELECT statements will be allowed.

CloseHandle(dstHandle1);
//DDL statements will be allowed.
//DML statements will be allowed.
//SELECT statements will be allowed.

D.無法關閉資料指標

下列範例會顯示未關閉的陳述式資料指標如何讓 OpenSqlFilestream() 無法開啟 BLOB 進行寫入存取。

TCHAR *sqlDBQuery =
TEXT("SELECT GET_FILESTREAM_TRANSACTION_CONTEXT(),")
TEXT("Chart.PathName() FROM Archive.dbo.Records");

//Execute a long-running Transact-SQL statement. Do not allow
//the statement to complete before trying to
//open the file.

SQLExecDirect(hstmt, sqlDBQuery, SQL_NTS);

//Before you call OpenSqlFilestream() any open files
//that the Cursor the Transact-SQL statement is using
// must be closed. In this example,
//SQLCloseCursor(hstmt) is not called so that
//the transaction will indicate that there is a file
//open for reading. This will cause the call to
//OpenSqlFilestream() to fail because the file is
//still open.

HANDLE srcHandle =  OpenSqlFilestream(srcFilePath,
     Write, 0,  transactionToken,  cbTransactionToken,  0);

//srcHandle will == INVALID_HANDLE_VALUE because the
//cursor is still open.

請參閱

參考

使用 OpenSqlFilestream 存取 FILESTREAM 資料

概念

使用 Multiple Active Result Sets (MARS)