Microsoft SQL Server 2008 R2 Unleashed- P166 pptx

Allowing both T-SQL and Win32 access to FILESTREAM data by checking the Enable FILESTREAM for File I/O Streaming Access option and providing a Windows share name to be used to access the

FIGURE 42.1 Setting FILESTREAM options in SQL Server Configuration Manager

file system for storing FILESTREAM data You have three options for how FILESTREAM

functionality will be enabled:

Allowing only T-SQL access (by checking only the Enable FILESTREAM for

Transact-SQL Access option)

Allowing both T-SQL and Win32 access to FILESTREAM data (by checking the Enable

FILESTREAM for File I/O Streaming Access option and providing a Windows share

name to be used to access the FILESTREAM data) This allows Win32 file system

interfaces to provide streaming access to the data

Allowing remote clients to have access to the FILESTREAM data that is stored on this

share (by selecting the Allow Remote Clients to Have Streaming Access to

FILESTREAM Data option)

NOTE

You need to be Windows Administrator on a local system and have sysadminrights to

enable FILESTREAM for SQL Server

After you enable FILESTREAM in SQL Server Configuration Manager, a new share is

created on the host system with the name specified This share is intended only to allow

very low-level streaming interaction between SQL Server and authorized clients It is

recommended that only the service account used by the SQL Server instance should have

access to this share Also, because this change takes place at the OS level and not from

within SQL Server, you need to stop and restart the SQL Server instance for the change to

take effect

After restarting the SQL Server instance to enable FILESTREAM at the Windows OS level,

you next need to enable FILESTREAM for the SQL Server Instance You can do this either

through SQL Server Management Studio or via T-SQL To enable FILESTREAM for the SQL

Server instance using SQL Server Management Studio, right-click on the SQL Server

instance in the Object Explorer, select Properties, select the Advanced page, and set the

Filestream Access Level property as shown in Figure 42.2 The available options are

Disabled (0)—FILESTREAM access is not permitted.

Transact SQL Access Enabled (1)—FILESTREAM data can be accessed only by

T-SQL commands

Full Access Enabled (2)—Both T-SQL and Win32 access to FILESTREAM data are

permitted

You can also optionally enable FILESTREAM for the SQL Server instance using the

sp_Configuresystem procedure, specifying the ’filestream access level’as the setting

and passing the option of 0(disabled),1(T-SQL access), or 2(Full access) The following

example shows full access being enabled for the current SQL Server instance:

EXEC sp_configure ‘filestream access level’, 2

GO

RECONFIGURE

GO

FIGURE 42.2 Enabling FILESTREAM for a SQL Server Instance in SSMS

After you configure the SQL Server instance for FILESTREAM access, the next step is to set

up a database to store FILESTREAM data

Setting Up a Database for FILESTREAM Storage

After you enable FILESTREAM for the SQL Server instance, you can store FILESTREAM data

in a database by creating a FILESTREAMfilegroup You can do this when creating the

data-base or by adding a new filegroup to an existing datadata-base The filegroup designated for

FILESTREAM storage must include the CONTAINS FILESTREAMclause and be defined The

code in Listing 42.18 creates the Customerdatabase and then adds a FILESTREAMfilegroup

LISTING 42.18 Setting Up a Database for FILESTREAM Storage

CREATE DATABASE Customer

ON ( NAME=’Customer_Data’,

FILENAME=’C:\SQLData\Customer_Data1.mdf’,

SIZE=50,

MAXSIZE=100,

FILEGROWTH=10)

LOG ON ( NAME=’Customer_Log’,

FILENAME=’C:\SQLData\Customer_Log.ldf’,

SIZE=50,

FILEGROWTH=20%)

GO

ALTER DATABASE Customer

ADD FILEGROUP Cust_FSGroup CONTAINS FILESTREAM

GO

ALTER DATABASE Customer

ADD FILE ( NAME=custinfo_FS,

FILENAME = ‘G:\SQLData\custinfo_FS’)

TO FILEGROUP Cust_FSGroup

GO

Notice in Listing 42.18 the FILESTREAMfilegroup points to a file system folder rather than

an actual file This folder must not exist already (although the path up to the folder must

exist); SQL Server creates the FILESTREAM folder (for example, in Listing 42.18, the

custinfo_FSfolder is created automatically by SQL Server in the G:\SQLDatafolder) The

FILESTREAM files and file data actually end up being stored in the created folder A

FILESTREAMfilegroup is restricted to referencing only a single file folder

Using FILESTREAM Storage for Data Columns

Once FILESTREAM storage is enabled for a database, you can specify the FILESTREAM

attribute on a varbinary(max)column to indicate that a column should store data in the

FILESTREAMfilegroup on the file system When columns are defined with the FILESTREAM

attribute, the Database Engine stores all data for that column on the file system instead of

in the database file In addition to a varbinary(max)column with the FILESTREAM

attribute, tables used to store FILESTREAM data also require the existence of a UNIQUE

ROWGUIDCOL, as shown in Listing 42.19, which creates a custinfotable on the FILESTREAM

filegroup.CUSTDATAis defined as the FILESTREAMcolumn, and ID is defined as the unique

ROWGUIDcolumn

LISTING 42.19 Creating a FILESTREAM-Enabled Table

CREATE TABLE CUSTINFO

(ID UNIQUEIDENTIFIER ROWGUIDCOL NOT NULL UNIQUE,

CUSTDATA VARBINARY (MAX) FILESTREAM NULL )

FILESTREAM_ON Cust_FSGroup

Each table created with a FILESTREAMcolumn(s) creates a new subfolder in the FILESTREAM

filegroup folder, and each FILESTREAMcolumn in the table creates a separate subfolder

under the tablefolder These column folders are where the actual FILESTREAM files are

stored Initially, these folders are empty until you start adding rows into the table A file is

created in the columnsubfolder for each row inserted into the table with a non-NULLvalue

for the FILESTREAMcolumn

NOTE

For more detailed information on how FILESTREAM data is stored and managed, see

Chapter 34

To ensure that SQL Server creates a new, blank file within the FILESTREAM storage folder

for each row inserted in the table, you can specify a default value of0xfor the

FILESTREAMcolumn:

alter table CUSTINFO add constraint custdata_def default 0x for CUSTDATA

Creating a default is not required if all access to the FILESTREAM data is going to be done

through T-SQL However, if you will be using Win32 streaming clients to upload file

contents into the FILESTREAMcolumn, the file needs to exist already Without the default

to ensure creation of a “blank” file for each row, new files would have to be created first

by inserting contents directly through T-SQL before they could be accessed via Win32

client streaming applications

To insert data into a FILESTREAMcolumn, you use a normal INSERTstatement and provide

avarbinary(max)value to store into the FILESTREAMcolumn:

INSERT CUSTINFO (ID, CUSTDATA)

VALUES (NEWID(), CONVERT(VARBINARY(MAX), REPLICATE (‘CUST DATA’, 100000)))

To retrieve FILESTREAM data, you can use a simple T-SQL SELECTstatement, although you

may need to convert the varbinary(max)tovarcharto be able to display text data:

select ID, CONVERT(varchar(40), CUSTDATA) as CUSTDATA

from CUSTINFO

go

ID CUSTDATA

-

-FA67BF05-51B5-4BA7-A383-7F88DAAE9C49 CUST DATACUST DATACUST DATACUST DATACUST

The preceding examples work fine if the FILESTREAM data is essentially text data;

however, neither SQL Server Management Studio nor SQL Server itself really has any user

interface, or native way, to let you stream the contents of an actual file into a table that’s

been marked with the FILESTREAMattribute on one of your varbinary(max)columns In

other words, if you have a .jpgor.mp3file that you want to store within SQL Server,

there’s no native functionality to convert that image’s byte stream into something that

you could put, for example, into a simple INSERTstatement To read or store this type of

data, you need to use Win32 to read and write data to a FILESTREAM BLOB Following are

the steps you need to perform in your client applications:

1 Read the FILESTREAM file path

2 Read the current transaction context

3 Obtain a Win32 handle and use the handle to read and write data to the

FILESTREAM BLOB

Each cell in a FILESTREAM table has a file path associated with it You can use thePATHNAME

property to retrieve the file path of avarbinary(max)column in a T-SQL statement:

DECLARE @filePath varchar(max)

SELECT @filePath = CUSTDATA.PathName()

FROM CUSTINFO

WHERE ID = ‘FA67BF05-51B5-4BA7-A383-7F88DAAE9C49’

PRINT @filepath

go

\\LATITUDED830-W7\FILESTREAM\v1\Customer\dbo\CUSTINFO\CUSTDATA

\FA67BF05-51B5-4BA7-A383-7F88DAAE9C49

Next, to obtain the current transaction context and return it to the client application, use

theGET_FILESTREAM_TRANSACTION_CONTEXT()T-SQL function:

BEGIN TRAN

SELECT GET_FILESTREAM_TRANSACTION_CONTEXT()

After you obtain the transaction context, the next step in your application code is to

obtain a Win32 file handle to read or write the data to theFILESTREAMcolumn To obtain

a Win32 file handle, you call theOpenSqlFilestreamAPI The returned handle can then be

passed to any of the following Win32 APIs to read and write data to a FILESTREAM BLOB:

ReadFile

WriteFile

TransmitFile

SetFilePointer

SetEndOfFile

FlushFileBuffers

To summarize, the steps you perform to upload a file to aFILESTREAMcolumn are as follows:

1 Start a new transaction and obtain the transaction context ID that can be used to

initiate the Win32 file-streaming process

2 Execute a SqlDataReaderconnection to pull back the full path (in SQL Server) of the

FILESTREAM file to which you will be uploading data

3 Initiate a straight file-streaming operation using the

System.Data.SqlTypes.SqlFileStreamclass

4 Create a new System.IO.FileStreamobject to read the file locally and buffer bytes

along to the SqlFileStreamobject until there are no more bytes to transfer

5 Close the transaction

NOTE

Because you’re streaming file contents via a Win32 process, you need to use

integrat-ed security to connect to SQL Server because native SQL logins can’t generate the

needed security tokens to access the underlying file system where the FILESTREAM

data is stored

To retrieve data from a FILESTREAMcolumn to a file on the client, you primarily follow the

same steps as you do for inserting data; however, instead you pull data from a

SqlFileStreamobject into a buffer and push it into a local FILESTREAMobject until there

are no more bytes left to retrieve

TIP

Refer to the “Managing FILESTREAM Data by Using Win32” topic in SQL Server 2008

R2 Books Online for specific C#, Visual Basic, and Visual C++ application code

exam-ples showing how to obtain a Win32 file handle and use it to read and write data to a

FILESTREAMcolumn

Sparse Columns

SQL Server 2008 provides a new space-saving storage option referred to as sparse columns.

Sparse columns can provide optimized and efficient storage for columns that contain

predominatelyNULLvalues The NULLvalues require no storage space, but these space

savings come at a cost of increased space for storing non-NULLvalues (an additional 2–4

bytes of space is needed for non-NULLvalues) For this reason, Microsoft recommends

using sparse columns only when the space saved is at least 20% to 40% However, the

consensus rule of thumb that is emerging from experience with sparse columns is that it is

best to use them only when more than 90% of the values are NULL

There are a number of restrictions and limitations regarding the use of sparse columns,

including the following:

Sparse columns cannot be defined with the ROWGUIDCOLorIDENTITYproperties

Sparse columns cannot be defined with a default value

Sparse columns cannot be used in a user-defined table type

Although sparse columns allow up to 30,000 columns per table, the total row size is

reduced to 8,018 bytes due to the additional overhead for sparse columns

If a table has sparse columns, you can’t compress it at either the row or page level

Columns defined with the geography,geometry,text,ntext,timestamp,image, or

user-defined data types cannot be defined as sparse columns

You can’t define varbinary(max)fields that use FILESTREAM storage as sparse

columns

You can’t define a computed column as sparse, but you can use a sparse column in

the calculation of a computed column

A table cannot have more than 1,024 non-sparse columns

Column Sets

Column sets provide an alternative way to view and work with all the sparse columns in a

table The sparse columns are aggregated into a single untyped XML column, which

simplifies working with many sparse columns in a table The XML column used for a

column set is similar to a calculated column in that it is not physically stored, but unlike

calculated columns, it is updateable

There are some restrictions on column sets:

You cannot add a column set to a table that already has sparse columns

You can define only one column set per table

Constraints or default values cannot be defined on a column set

Computed columns cannot contain column set columns

A column set cannot be changed; you must delete and re-create the column set

However, sparse columns can be added to the table after a column set has been

defined and is automatically included in the column set

Distributed queries, replication, and Change Data Capture do not support column sets

A column set cannot be part of any kind of index, including XML indexes, full-text

indexes, and indexed views

NOTE

Sparse columns and column sets are defined by using the CREATE TABLEorALTER

TABLEstatements This chapter focuses on using and working with sparse columns

For more information on defining sparse columns and column sets, see Chapter 24,

“Creating and Managing Tables.”

Working with Sparse Columns

Querying and manipulation of sparse columns is the same as for regular columns, with

one exception described later in this chapter There’s nothing functionally different about

a table that includes sparse columns, except the way the sparse columns are stored You

can still use all the standard INSERT,UPDATE, and DELETEstatements on tables with sparse

columns just like a table that doesn’t have sparse columns You can also wrap operations

on a table with sparse columns in transactions as usual

To work with sparse columns, let’s first create a table with sparse columns Listing 42.20

creates a version of the Producttable in the AdventureWorks2008R2database and then

populates the table with data from the Production.Producttable The Color,Weight, and

SellEndDatecolumns are defined as sparse columns (the source data contains a significant

number of NULLvalues for these columns) These columns are also defined as part of the

column set, ProductInfo

LISTING 42.20 Creating a Table with Sparse Columns

USE AdventureWorks2008R2

GO

CREATE TABLE Product_sparse

(

ProductID INT NOT NULL PRIMARY KEY,

ProductName NVARCHAR(50) NOT NULL,

Color NVARCHAR(15) SPARSE NULL,

Weight DECIMAL(8,2) SPARSE NULL,

SellEndDate DATETIME SPARSE NULL,

ProductInfo XML COLUMN_SET FOR ALL_SPARSE_COLUMNS

)

GO

INSERT INTO Product_sparse

(ProductID, ProductName, Color, Weight, SellEndDate)

SELECT ProductID, Name, Color, Weight, SellEndDate

FROM Production.Product

GO

You can reference the sparse columns in your queries just as you would any type of column:

SELECT productID, productName, Color, Weight, SEllEndDate

FROM Product_sparse

where ProductID < 320

go

productID productName Color Weight SEllEndDate

- - -

-1 Adjustable Race NULL NULL NULL

2 Bearing Ball NULL NULL NULL

3 BB Ball Bearing NULL NULL NULL

4 Headset Ball Bearings NULL NULL NULL

316 Blade NULL NULL NULL

317 LL Crankarm Black NULL NULL

318 ML Crankarm Black NULL NULL

319 HL Crankarm Black NULL NULL

Note, however, that if you use SELECT *in a query and the table has a column set defined

for the sparse columns, the column set is returned as a single XML column instead of the

individual columns:

SELECT *

FROM Product_sparse

where ProductID < 320

go

ProductID ProductName ProductInfo

- -

-1 Adjustable Race NULL

2 Bearing Ball NULL

3 BB Ball Bearing NULL

4 Headset Ball Bearings NULL

316 Blade NULL

317 LL Crankarm <Color>Black</Color>

318 ML Crankarm <Color>Black</Color>

319 HL Crankarm <Color>Black</Color>

You need to explicitly list the columns in the SELECTclause to have the result columns

returned as relational columns

When the column set is defined, you can also operate on the column set by using XML

operations instead of relational operations For example, the following code inserts a row

into the table by using the column set and specifying a value for Weightas XML:

INSERT Product_sparse(ProductID, ProductName, ProductInfo)

VALUES(5, ‘ValveStem’, ‘<Weight>.12</Weight>’)

go

SELECT productID, productName, Color, Weight, SEllEndDate

FROM Product_sparse

where productID = 5

go

productID productName Color Weight SEllEndDate

- -

-5 ValveStem NULL 0.12 NULL

Notice that NULLis assumed for any column omitted from the XML value, such as Color

andSellEndDatein this example

When updating a column set using an XML value, you must include values for all the

columns in the column set you want to set, including any existing values Any values not

specified in the XML string are set to NULL For example, the following query sets both

ColorandWeightwhereProductID = 5:

Update Product_sparse

set ProductInfo = ‘<Color>black</Color><Weight>.20</Weight>’

where productID = 5

SELECT productID, productName, Color, Weight, SEllEndDate

FROM Product_sparse

where productID = 5

go

productID productName Color Weight SEllEndDate

- -

-5 ValveStem black 0.20 NULL