Microsoft SQL Server 2008 R2 Unleashed- P47 doc

ptg 404 CHAPTER 14 Database Backup and Restore your database. Databases that are set to simple recovery mode have limited options for database restore. Databases that are in full recovery mode and have frequent backups have many more restore options. Following are the basic options for restore: . Restore an entire database. . Perform a partial restore. . Restore a file or page from a backup. . Restore a transaction log. . Restore a database to a point in time by using a database snapshot. The following sections delve further into the restore options listed here. They focus on the means for accomplishing these restores and some of the common restore scenarios you might encounter. Restores with T-SQL The command to restore a database in SQL Server is aptly named RESTORE. The RESTORE command is similar to the BACKUP command in that it can be used to restore a database, part of a database, or a transaction log. You restore an entire database or part of a database by using the RESTORE DATABASE syntax. You do transaction log restores by using the RESTORE TRANSACTION syntax. Database Restores with T-SQL Listing 14.6 shows the full syntax for RESTORE DATABASE. LISTING 14.6 RESTORE DATABASE Syntax To Restore an Entire Database from a Full database backup (a Complete Restore): RESTORE DATABASE { database_name | @database_name_var } [ FROM <backup_device> [ , n ] ] [ WITH [ { CHECKSUM | NO_CHECKSUM } ] [ [ , ] { CONTINUE_AFTER_ERROR | STOP_ON_ERROR } ] [ [ , ] ENABLE_BROKER ] [ [ , ] ERROR_BROKER_CONVERSATIONS ] [ [ , ] FILE = { file_number | @file_number } ] [ [ , ] KEEP_REPLICATION ] [ [ , ] MEDIANAME = { media_name | @media_name_variable } ] [ [ , ] MEDIAPASSWORD = { mediapassword | @mediapassword_variable } ] [ [ , ] MOVE ‘logical_file_name’ TO ‘operating_system_file_name’ ] [ , n ] [ [ , ] NEW_BROKER ] [ [ , ] PARTIAL ] [ [ , ] PASSWORD = { password | @password_variable } ] [ [ , ] { RECOVERY | NORECOVERY | STANDBY = Download from www.wowebook.com ptg 405 Restoring Databases and Transaction Logs 14 {standby_file_name | @standby_file_name_var } } ] [ [ , ] REPLACE ] [ [ , ] RESTART ] [ [ , ] RESTRICTED_USER ] [ [ , ] { REWIND | NOREWIND } ] [ [ , ] STATS [ = percentage ] ] [ [ , ] { STOPAT = { date_time | @date_time_var } | STOPATMARK = { ‘mark_name’ | ‘lsn:lsn_number’ } [ AFTER datetime ] | STOPBEFOREMARK = { ‘mark_name’ | ‘lsn:lsn_number’ } [ AFTER datetime ] } ] [ [ , ] { UNLOAD | NOUNLOAD } ] ] Once again, there are many available options for restoring a database, but a simple restore is fairly straightforward. The following example demonstrates a full restore of the AdventureWorks2008 database: RESTORE DATABASE [AdventureWorks2008] FROM DISK = N’C:\mssql2008\backup\AdventureWorks2008_FullRecovery.bak’ WITH FILE = 1, NOUNLOAD, REPLACE, STATS = 10 For more sophisticated restores, you can specify options following the WITH clause. Table 14.2 briefly describes these options. Many of the options are the same as for the BACKUP command and provide similar functionality. TABLE 14.2 RESTORE DATABASE Options Option Description CHECKSUM | NO_CHECKSUM When CHECKSUM is specified, a checksum is calcu- lated before the backup is restored. If the check- sum validation fails, the restore fails as well. The default is NO_CHECKSUM. STOP_ON_ERROR | CONTINUE_AFTER_ERROR The STOP_ON_ERROR option, which is the default, causes the backup to fail if an error is encoun- tered. CONTINUE_AFTER_ERROR allows the restore to continue if an error is encountered. ENABLE_BROKER This option starts the Service Broker so that messages can be received. Download from www.wowebook.com ptg 406 CHAPTER 14 Database Backup and Restore TABLE 14.2 RESTORE DATABASE Options Option Description ERROR_BROKER_CONVERSATIONS Service Broker conversations with the database being restored are ended, with an error stating that the database is attached or restored. FILE = { file_number | @file_number } This option identifies the backup set number to be restored from the backup media. The default is 1, which indicates the latest backup set. KEEP_REPLICATION This option prevents replication settings from being removed during a restore operation. This is impor- tant when setting up replication to work with log shipping. MEDIANAME This is a 128-character name for the backup media. If it is specified, the target media must match this name. MEDIAPASSWORD This is a password for the media set. If the media was created with a password, the password must be supplied to restore from that media. MOVE This option causes the specified logical_file_name to be moved from its original file location to another location. NEW_BROKER This option creates a new service_broker_guid. PARTIAL This option causes a partial restore to occur that includes the primary filegroup and any specified secondary filegroup(s). PASSWORD This password is specific to the backup set. If a password was used when creating the backup set, a password must be used to restore from the media set. RECOVERY | NORECOVERY | STANDBY The RECOVERY option, which is the default, restores the database so that it is ready for use. NORECOVERY renders the database inaccessible but able to restore additional transaction logs. The STANDBY option allows additional transaction logs to be applied but the database to be read. These options are discussed in more detail later in this section. Download from www.wowebook.com ptg 407 Restoring Databases and Transaction Logs 14 Various options are utilized in the “Restore Scenarios” section, later in this chapter. Those restore scenarios provide a frame of reference for the options and further meaning about what they can accomplish. Transaction Log Restores with T-SQL The syntax details and options for restoring a transaction log backup are similar to those for RESTORE BACKUP. The options not available with RESTORE LOG include ENABLE_BROKER, ERROR_BROKER_CONVERSATIONS, NEW_BROKER,and PARTIAL. The RECOVERY | NORECOVERY | STANDBY options are particularly important when perform- ing transaction log restores and also when restoring a database that will have transaction TABLE 14.2 RESTORE DATABASE Options Option Description REPLACE This option causes the database to be created with the restore, even if the database already exists. RESTART This option allows a previously interrupted restore to restart where it was stopped. RESTRICTED_USER This option restricts access to the database after it has been restored. Only members of the db_owner, dbcreator, or sysadmin role can access it. REWIND | NOREWIND This option is used for tape operations. REWIND, which is the default, causes the tape to be released and rewound. STATS This option causes completion statistics to be displayed at the specified interval to assess progress. STOPAT | STOPATMARK | STOPBEFOREMARK This option causes a restore to recover to a speci- fied date/time or to recover to a point defined by a specific transaction. The STOPAT option restores the database to the state it was in at the date and time. The STOPATMARK and STOPBEFOREMARK options restore based on the specified marked transaction or LSN. UNLOAD | NOUNLOAD This option is used for tape operations. NOUNLOAD cause the tape to remain in the tape drive after a restore completes. UNLOAD, which is the default, causes the tape to be rewound and unloaded when the restore completes. Download from www.wowebook.com ptg 408 CHAPTER 14 Database Backup and Restore logs applied. If these options are used incorrectly, you can render your database inaccessi- ble or unable to restore subsequent transaction log backups. With the RECOVERY option, any uncommitted transactions are rolled back, and the database is made available for use. When a restore (of either a database or transaction log) is run with this option, no further transaction logs can be applied. The NORECOVERY and STANDBY options do allow subsequent transaction logs to be applied. When the NORECOVERY option is specified, the database is completely unavailable after the restore and is left in a restoring state. In this state, you cannot read the database, update the database, or obtain information about the database, but you can restore transaction logs. With the STANDBY option, the database is left in a read-only state that allows some data- base access. standby_file_name must be specified with the STANDBY option. The standby file contains uncommitted transactions rolled back to place the database in a consistent state for read operations. If subsequent transaction log backups are applied to the STANDBY database, the uncommitted transactions in the standby file are reapplied to the database. CAUTION Take note of the standby_file_name name used when restoring with the STANDBY option and make sure the file is secure. If another restore operation is performed and the same standby_file_name is used, the previous standby file is overwritten. The database cannot be fully recovered without the standby file, so you have to perform all the restore operations again. We speak from personal experience on this one. During a data recovery drill, for a large database (approximately 1TB), we spent hours restoring the transaction logs on a set of log-shipped databases. We manually restored the last log to be applied to place the database in STANDBY mode. Another database also in the data recovery drill was also placed in STANDBY, and unfortunately, the same standby file was used on this data- base. This caused more than one person a very long night. Be careful! Some of the other options of the RESTORE DATABASE command are covered in the “Restore Scenarios” section, later in this chapter. Once again, many of these options are not required for most types of restores. For example, the following command uses basic options to restore a transaction log backup to the AdventureWorks2008 database: RESTORE LOG [AdventureWorks2008] FROM DISK = N’C:\mssql2008\backup\AdventureWorks2008\AdventureWorks2008_backup_200906091215.trn’ WITH FILE = 1, NOUNLOAD, STATS = 10, NORECOVERY Typically, the individual restore commands you will use are along the lines of the preced- ing example. The restores become more complicated when many restores of different types are involved in a recovery option. Fortunately, SSMS can help ease this pain. Download from www.wowebook.com ptg 409 Restoring Databases and Transaction Logs 14 Restoring by Using SSMS The restore capabilities in SSMS are comprehensive and can reduce the amount of time needed to perform a restore and limit the number of errors. This is partly due to the fact that SSMS keeps track of the backups that have occurred on a server. When a restore oper- ation is requested for a database, SQL Server reads from its own system tables and presents a list of backups that it knows about that can be restored. In situations in which many files need to be restored, SSMS can be an invaluable tool. You access the restore functions in SSMS by right-clicking the database in the Object Explorer and selecting Tasks and then Restore. The options available for restore include Database, File and Filegroups, and Transaction Log. Which restore options are enabled depends on the state of the database being restored. The Transaction Log option is disabled for databases that were restored with the RECOVERY option or are set to simple recovery mode. Figure 14.6 shows an example of the restore screen that is displayed when you select a database restore for the AdventureWorks2008 database. The Restore Database window can show more than one type of backup, depending on what is available. The first backup shown in Figure 14.6 is a full backup, followed by a series of transaction log backups. The beauty of this screen is that the backups are shown in the order in which they should be applied. This order is very important with restores FIGURE 14.6 A database restore with SSMS. Download from www.wowebook.com ptg 410 CHAPTER 14 Database Backup and Restore because they must be applied in the order in which they occurred. You can choose to apply all the backups or selectively choose the backups you want to apply. If you uncheck the first full database backup, all subsequent log backups are unchecked as well. If you recheck the full database backup and click one of the transaction log backups toward the bottom of the list, all the required backups that happened prior to the selected backups are also selected. Figure 14.7 shows an example or the Options page of the Restore Database window for the AdventureWorks2008 database. The Options page allows you to specify many of the T-SQL RESTORE options reviewed previously. The Overwrite the Existing Database option is equiv- alent to the REPLACE parameter and forces a replacement of the restored database if it exists already. The Preserve the Replication Settings option is equivalent to KEEP_REPLICATION. The Restrict Access to the Restored Database option is the same as using the RESTRICTED_USER option with the T-SQL RESTORE command. The Prompt Before Restoring Each Backup option does not have a T-SQL equivalent; it displays a prompt before restoring each backup set to ask whether you want to restore it. The last three options on the Options page relate the recovery state of the last backup set restored. The first option is synonymous with the RECOVERY option, the second option is the same as NORECOVERY, and the last option is equivalent to the STANDBY option. The standby filename must be supplied with the STANDBY option and defaults to the default backup directory for the server. By default, the name of the file contains the name of the database being restored. FIGURE 14.7 Restore options with SSMS. Download from www.wowebook.com ptg 411 Restoring Databases and Transaction Logs 14 TIP You sho uld cl ick the Script button available on the Restor e Database window if yo u want to see what is going on under the hood of the SSMS restores or want to run a restore later. You can learn a lot about the T-SQL options and how they work by script- ing out the commands. Restore Information Backup files and system tables contain a wealth of information about what can be restored or already has been restored. You can retrieve information from the backup files by using variations of the RESTORE command. These variations do not actually perform the restore operation but provide information about the backups that can be restored. The RESTORE commands and some useful system tables are detailed in the following sections. The RESTORE FILELISTONLY Command The RESTORE FILELISTONLY command returns a result set that contains a list of the data- base and log files contained in the backup. An example of this command follows: RESTORE FILELISTONLY FROM DISK = ‘C:\mssql2008\backup\AdventureWorks2008_Partial.bak’ The results from this type of restore include the logical and physical filenames, the type of each file, and the size of each file. The RESTORE HEADERONLY Command The RESTORE HEADERONLY command returns a result set that contains the backup header data for all backup sets on the specified backup device. This command is useful when multiple backup sets are written to the same device. An example of this command follows: RESTORE HEADERONLY FROM DISK = ‘C:\mssql2008\backup\AdventureWorks2008_Partial.bak’ More than 50 columns are returned in the result set. Some particularly useful pieces of information include the start and finish time for the backup, recovery mode when the backup was taken, type of backup, and name of the computer from which the backup was performed. The RESTORE VERIFYONLY Command The RESTORE VERIFYONLY command verifies that a backup set is complete and readable. The restore does not attempt to verify the structure of the data in the backups, but it has been enhanced to run additional checks on the data. The checks are designed to increase the probability of detecting errors. An example of this command follows: Download from www.wowebook.com ptg 412 CHAPTER 14 Database Backup and Restore RESTORE VERIFYONLY FROM DISK = ‘C:\mssql2008\backup\AdventureWorks2008_Partial.bak’ /*Result from the prior RESTORE VERIFYONLY command The backup set on file 1 is valid. */ The results from the prior example show that the RESTORE VERIFYONLY command does not contain much output, but the value of this command is in helping ensure that the backups are sound. Backup and Restore System Tables The system tables for backups and restores are found in the msdb system database. These system tables are used to keep historical information about the backups and restores that have occurred on the server. These system tables are listed in Table 14.3. Refer to “Backup and Restore Tables” in the “System Tables” section of SQL Server Books Online for a detailed description of each table, including each column that can be retrieved. TABLE 14.3 Backing Up and Restoring System Tables msdb System Table Description backupfile Contains one row for each data or log file of a database. backupfilegroup Contains one row for each filegroup in a database at the time of backup. backupmediafamily Contains a row for each media family. backupmediaset Contains one row for each backup media set. backupset Contains a row for each backup set. logmarkhistory Contains one row for each marked transaction that has been committed. restorefile Contains one row for each restored file. These include files restored indi- rectly, by filegroup name. restorefilegroup Contains one row for each restored filegroup. restorehistory Contains one row for each restore operation. suspect_pages Contains one row per page that failed with an 824 error (with a limit of 1,000 rows). sysopentapes Contains one row for each currently open tape device. Download from www.wowebook.com ptg 413 Restoring Databases and Transaction Logs 14 You are able to query these tables to obtain a variety of information related to backups and restores. You can tailor these queries to look at a specific database or a specific time frame. The following example retrieves restore information for the AdventureWorks2008 database: select destination_database_name ‘database’, h.restore_date, restore_type, cast((backup_size/1024)/1024 as numeric(8,0)) ‘backup_size MB’, f.physical_device_name from msdb restorehistory h (NOLOCK) LEFT JOIN msdb backupset b (NOLOCK) ON h.backup_set_id = b.backup_set_id LEFT JOIN msdb backupmediafamily f (NOLOCK) ON b.media_set_id = f.media_set_id where h.restore_date > getdate() - 5 and UPPER(h.destination_database_name) = ‘AdventureWorks2008’ order by UPPER(h.destination_database_name), h.restore_date desc This example displays information related to restores that have been executed in the past five days for the AdventureWorks2008 database. The restore date, type of restore, size of the backup, and physical location of the file used for the restore are displayed when you run this query. CAUTION Queries against system tables are acceptable and can provide a wealth of information, but you need to exercise caution whenever you are dealing with a system table. SQL Server uses these tables, and problems can occur if the values in them are changed or their physical structure is altered. Backup and Restore Report A set of standard reports that come with SQL Server 2008 provide a variety of information about your databases, including recent restores and backups. You can access these reports by right-clicking on a database in the SSMS Object Explorer, then Reports, and then Standard Reports. You see over a dozen reports ready for you to run. A report particularly useful for obtaining restore and backup information is named Backup and Restore Events. This report details the latest backup and restore events that have occurred on a particular database. An example of this report is shown in Figure 14.8. The interactive report allows you to drill down into each backup or restore event to obtain more information. For example, the restore information shown in Figure 14.8 was obtained by clicking on the plus button next to the Successful Restore Operations label. You can then drill down into an individual restore to obtain more information, including the physical files involved in the operation. Download from www.wowebook.com . transaction log backup to the AdventureWorks2008 database: RESTORE LOG [AdventureWorks2008] FROM DISK = N’C:mssql2008ackupAdventureWorks2008AdventureWorks2008_backup_200906091215.trn’ WITH FILE. demonstrates a full restore of the AdventureWorks2008 database: RESTORE DATABASE [AdventureWorks2008] FROM DISK = N’C:mssql2008ackupAdventureWorks2008_FullRecovery.bak’ WITH FILE = 1, NOUNLOAD,. some of the common restore scenarios you might encounter. Restores with T -SQL The command to restore a database in SQL Server is aptly named RESTORE. The RESTORE command is similar to the BACKUP