-- Truncated for brevity ALTER DATABASE AdventureWorks SET MULTI_USER; GO Using the DBCC SHRINKFILE Option to Reclaim Database Space DBCC SHRINKFILE shrinks a database file or a log fil
Trang 1Service Broker Msg 9675, State 1: Message Types analyzed: 14.
Service Broker Msg 9676, State 1: Service Contracts analyzed: 6.
Service Broker Msg 9667, State 1: Services analyzed: 3.
Service Broker Msg 9668, State 1: Service Queues analyzed: 3.
Service Broker Msg 9669, State 1: Conversation Endpoints analyzed: 0 Service Broker Msg 9674, State 1: Conversation Groups analyzed: 0.
Service Broker Msg 9670, State 1: Remote Service Bindings analyzed: 0 Service Broker Msg 9605, State 1: Conversation Priorities analyzed: 0 DBCC results for 'sys.sysrscols'.
There are 1483 rows in 17 pages for object "sys.sysrscols".
DBCC results for 'sys.sysrowsets'.
There are 286 rows in 3 pages for object "sys.sysrowsets".
DBCC results for 'sys.sysallocunits'.
There are 334 rows in 5 pages for object "sys.sysallocunits".
DBCC results for 'sys.sysfiles1'.
(Truncated for brevity)
ALTER DATABASE AdventureWorks
SET MULTI_USER;
GO
Using the DBCC
SHRINKFILE Option to Reclaim Database Space
DBCC SHRINKFILE shrinks a database file or a log file by rearranging data in the file to reclaim empty space It can also move all data from a data file to another data file in the same filegroup, allowing you to remove the empty file Using DBCC SHRINKFILE, you can shrink the file to a smaller size than its minimum size setting The minimum size setting will then be reset to reflect the actual size Use the syntax shown in Example 7.20 to run DBCC SHRINKFILE
Example 7.20 Using the DBCC SHRINKFILE—Syntax
DBCC SHRINKFILE ( file_name | file_id, [EMPTYFILE],
[target_size], [NOTRUNCATE | TRUNCATEONLY] )
[ WITH NO_INFOMSGS]
When running DBCC SHRINKFILE, you can specify various options to alter the command behavior You must specify the logical file name or file ID of the database or log file you wish to manipulate When the EMPTYFILE option is
Trang 2spec-ified, the DBCC moves all data from the specified file to other files in the same
filegroup SQL Server will no longer write to the file you have just emptied,
allow-ing you to remove the empty file usallow-ing the ALTER DATABASE statement
You can specify the target_size in megabytes The DBCC will then attempt to
shrink the file to the target size It does so by moving all data from throughout the
end pages to free space earlier in the file The file shrinkage will only be achieved if
enough free space is available in the file
The NOTRUNCATE option specifies that although the data in the file will be
rearranged, the free space will not be released back to the operating system This
means that the actual file size of the file will not change On the other hand,
TRUNCATEONLY will rearrange the data and reclaim the free space to the
oper-ating system, thereby shrinking the file TRUNCATEONLY ignores the target_size,
reclaiming all possible space Both NOTRUNCATE and TRUNCATEONLY are
applicable only to database files
The NO_INFOMSGS specifies that no informational messages are to be shown
by the DBCC
Example 7.21 demonstrates the use of DBCC SHRINKFILE
Example 7.21 Using the DBCC SHRINKFILE
USE AdventureWorks;
GO
SELECT file_id, name
FROM sys.database_files;
GO
Reclaim all available free space from the data file
DBCC SHRINKFILE ('AdventureWorks_Data', TRUNCATEONLY);
Results:
DbId FileId CurrentSize MinimumSize UsedPages EstimatedPages
- - - - -
(1 row(s) affected)
DBCC execution completed If DBCC printed error messages, contact your
system administrator.
Shrink the log file to 5 MB
DBCC SHRINKFILE (AdventureWorks_Log, 5);
GO
Empty a file
ALTER DATABASE AdventureWorks
ADD FILE ( NAME = NewData, FILENAME = 'C:\temp\newdata.ndf', SIZE = 5MB);
GO
Empty the data file.
Trang 3DBCC SHRINKFILE (NewData, EMPTYFILE);
GO
Remove the data file from the database.
ALTER DATABASE AdventureWorks
REMOVE FILE NewData;
GO
Results:
DbId FileId CurrentSize MinimumSize UsedPages EstimatedPages
- - - - -
(1 row(s) affected)
DBCC execution completed If DBCC printed error messages, contact your system administrator.
The file 'NewData' has been removed.
Backing Up and Restoring Data
Every organization that values its databases must have a disaster recovery strategy that works when needed The disaster recovery strategy defines procedures for backing up and restoring SQL Server databases Defining and adhering to the disaster recovery strategy is a primary task of any database administrator In this section, you will learn about various types of backup available with SQL Server, best practices for performing backups, and restoring databases from backup
Understanding
Database Recovery Models
The database recovery model determines how transaction logs are used by SQL Server for a specified database Your choice of recovery model affects which
operations are performed as nonlogged and whether the database can be recovered
to a point in time Three recovery models are available for SQL Server 2008
databases:
Simple recovery model
■
■
Full recovery model
■
■
Bulk-Logged recovery model
■
■
When the database recovery model is set to Simple, log files are reused as soon
as they become full This means that very little space is consumed by the transaction
Trang 4logs, and you don’t need to worry about log file management However, when a
database is set to Simple recovery model and the database file is lost, you will not be able to recover any changes made after the last full backup You will also not be able
to recover to a point in time as transaction details are stored in transaction logs that
have been overwritten in this case
The Full recovery model could be said to be the opposite of the Simple
recovery model Transaction logs are kept, and all transactions without exception are written to the logs This includes nonlogged operations like TRUNCATE
TABLE and SELECT…INTO Although you lose the performance advantages
of nonlogged operations with this recovery model, all data is recoverable
provided transaction logs are intact You can also restore to a point-in-time
if necessary
The Bulk-Logged recovery model is similar to Full recovery model, except that
nonlogged operations are performed as nonlogged This provides a performance
advantage for Bulk-Logged operations However, if a Bulk-Logged operation has
occurred since the last full backup, you will not be able to recover any changes
made since the last full backup The Bulk-Logged recovery model does not support
point-in-time recovery
In production environments, the full database recovery model is generally used as
it ensures maximum recoverability However, if the administrator wishes to perform a high performance nonlogged operation, they would temporarily switch the recovery
model to Bulk-Logged, perform the operation, switch the recovery model back to
Full, and perform a full backup The Full recovery model is the default when
creating databases in SQL Server
Backup Types
SQL Server databases can be backed up using the Backup Database Wizard or the
BACKUP DATABASE Transact-SQL statement By specifying a particular backup
type, you designate what data should be backed up For example, you may choose
to back up all data in a database or only the differences from the last full backup
All SQL Server backups are performed online This means that users can continue to
read and write to and from the database while the backup is being performed
However, backup is a resource and time intensive operation, especially for large
databases Therefore, backups should be scheduled at off-peak times to avoid
performance degradation Table 7.2 describes the types of backup available with
SQL Server 2008
Trang 5Backup Type Functionality Purpose
Full Backup Backup all data stored
in data files and a small part of the transaction log generated while the backup operation was taking place.
To back up an entire database that can be restored as a whole The most disk intensive and time consuming backup type.
Differential
Backup Backup the extents that were modified since the
last full backup.
Provides the ability
to create a frequent, incremental backup which can then be restored into
an earlier version of a database restored from full backup.
Partial Backup Backup of the primary
filegroup, all writeable filegroups, and
optionally specified read-only filegroups
Also available in differential partial backup, which backs
up only the extents changed since the last full or partial backup
of the corresponding filegroup.
Perform a more efficient, full or differential backup affecting only change-able data Especially useful for large partitioned databases consisting of historical data that does not change and current data that does Using partial backup, you can back up historical data only once and perform frequent partial backups
of the current data.
File or Filegroup A full backup of a
specified database file
or filegroup.
Allows you to granularly back up specific files or file groups for databases consisting of multiple files When database files are distributed across mul-tiple disks, you can restore the data file to the failed disk only, which is more efficient than restoring the entire database.
Table 7.2 SQL Server 2008 Backup Types
Continued