Win32 和 Transact-SQL 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。這包括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，允許或拒絕此要求。下表將顯示 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.