The Art of SQL Server FILESTREAM - Red Gate Software

Chapter 3: Accessing FILESTREAM Data from Client ApplicationsThe next argument in Listing 3-36 specifies additional flags that help the system tooptimize the requested file operation. The different values this parameter can take aredescribed below.• SQL_FILESTREAM_OPEN_NONE – Indicates that you do not want to specify anyadditional flags.• SQL_FILESTREAM_OPEN_FLAG_NO_WRITE_THROUGH – Instructs the system to sendwrites directly to disk, bypassing any intermediate caches.• SQL_FILESTREAM_OPEN_FLAG_ASYNC – Informs the system that you intend to usethe file for asynchronous reading and writing.• SQL_FILESTREAM_OPEN_FLAG_RANDOM_ACCESS – Informs the system that youmight access the file randomly. The system will use this information to optimize filecaching for random access.• SQL_FILESTREAM_OPEN_FLAG_SEQUENTIAL_SCAN – Informs the system thatyou will use the file sequentially. When this flag is specified, the system optimizes thefile operations on the basis that you will not access the file backwards or jump into arandom location in the file.• SQL_FILESTREAM_OPEN_FLAG_NO_BUFFERING – Requests the system to open thefile with no buffering support.The next argument in Listing 3-36 (transactionToken) is the FILESTREAM transactioncontext retrieved by calling T-SQL function GET_FILESTREAM_TRANSACTION_CONTEXT(). This is followed by another parameter, cbTransactionToken, whichspecifies the size of the buffer that stores the FILESTREAM transaction context.The final parameter in Listing 3-36 specifies the initial allocation size of the data filein bytes. This parameter is ignored when the file is opened for READ operation. If thisparameter is NULL, the system will use the default allocation size.128