Hướng dẫn học Microsoft SQL Server 2008 part 102 pdf

TABLE 41-2 Recovery Sequences Recovery Model Damaged Database File Damaged Transaction Log Simple 1 Restore full backup.. For example, under the full recovery model, the restore plan sel

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Recovery sequences

The two most important concepts about recovering a database are as follows:

■ A recovery operation always begins by restoring a full backup and then restores any additional differential or transactional backups The restore never copies only yesterday’s work It restores the entire database up to a certain point

■ There’s a difference between restore and recover A restore copies the data back into the database and leaves the transactions open Recovery is the process of handling the transactions

left open in the transaction log If a database-recovery operation requires that four files be restored, only the last file is restoredWITH RECOVERY

Only logins who are members of thesysadminsfixed server role can restore a database that doesn’t

currently exist.sysadminsanddb_ownerscan restore databases that do currently exist

The actual recovery effort depends on the type of damage and the previous recovery plans Table 41-2 is

a comparative listing of recovery operations

Performing the restore with Management Studio

As with theBACKUPcommand, there are numerous ways to launch the restore form within Management

Studio:

Select the database to be backed up From the context or Action menu select Tasks➪ Restore ➪

Database to open the SQL Server Restore Database form

TABLE 41-2

Recovery Sequences

Recovery Model Damaged Database File Damaged Transaction Log

Simple 1) Restore full backup

2) Restore latest differential backup (if needed)

It is very likely there are unapplied transactions lost with the transaction log and the database is inconsistent It

is recommended to fall back on your backups and use the steps docu-mented for ‘‘damaged database file.’’

Full or

Bulk-logged

1) Back up current transaction log with NO_TRUNCATEoption*

2) Restore full backup

4) Restore all the transaction-log backups since the last differential or full backup All committed transactions will be recovered

1) Restore full backup

3) Restore all the transaction-log backups since the last differential or full backup

Transactions made since the last backup will be lost

*If the database is using the bulk-logged recovery model and a bulk-insert operation occurred since the last

transaction-log backup, the backup will fail Transactions that occurred after the transaction-log backup will not

be recoverable.

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The Restore Database form, shown in Figure 41-6, does a great job of intelligently navigating the

poten-tial chaos of the backup sequences, and it always offers only legal restore options

FIGURE 41-6

Only the correct sequence of restoring from multiple backup files is possible from Management

Studio’s Restore Database form

The selection you make at the top of the form is the name of the database after the restore

The Restore Database form can restore database backups, file backups, or backups from a device (e.g a

tape drive) The Restore Wizard will present a hierarchical tree of backups, while the filegroups or file

restore lists the files and must be manually restored in the correct order

The ‘‘Select the backup sets to restore’’ option displays the available backups Management Studio

uses the backup history in themsdbdatabase and creates a restore plan For example, under the full

recovery model, the restore plan selects the full database backup followed by the most recent differential

database backup (if available), followed by subsequent log backups

If the backup history, stored inmsdb, is not available — because the server is being rebuilt or the

database is being restored to a different server — then use the Restore: From Device option to manually

select the specific backup disk file and backup instance within the file

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The process of one full backup, the second differential backup, and the following 15 transaction-log

backups can be correctly sequenced by selecting the final transaction log to be restored Restoring the 17

backup files is performed with a single click of the OK button

If one of the backup files being restored is a transaction log, the Point in Time Restore option becomes

available because only a transaction log can restore some of the transactions The point-in-time restore

will restore all transactions committed before the time selected

The Options page of the Restore Database form is shown in Figure 41-7

FIGURE 41-7

The Options page of the Restore Database form

The Options page of the Restore Database dialog offers a few significant options:

■ ‘‘Overwrite the existing database’’ disables a safety check that prevents Database A backup from being restored as Database B and accidentally overwriting an existing Database B

■ ‘‘Preserve the replication settings’’ preserves the replication settings when restoring a published database on a different SQL Server (other than the SQL Server where the database was cre-ated) This option is available only with the ‘‘Leave the database ready for use by rolling back the uncommitted transactions’’ option

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■ ‘‘Prompt before restoring each backup’’ prompts before continuing to restore the next backup

in the restore sequence This option is useful when you are restoring from tape backups and

need to swap tapes

■ ‘‘Restrict access to the restored database’’ restricts access to the restored database only to

members ofdb_owner,dbcreatoror sysadmin

■ Because it is very possible that the database is being restored to a different file location than

the original backup, the ‘‘Restore the database files as’’ section in the Options tab includes a

way to assign new file locations

■ ‘‘Leave the database ready for use by rolling back the uncommitted transactions’’ should be

used for restoring the final backup This option recovers the database and does not allow

additional transaction logs to be restored

■ ‘‘Leave the database non-operational, and do not roll back the uncommitted transactions’’

enables you to restore additional backups If you select this option, the ‘‘Preserve replication

settings’’ option is unavailable

■ ‘‘Leave the database in read-only mode’’ leaves the database in a standby mode in which the

database is available for limited read-only access

If only certain files or filegroups are being restored, then select Tasks➪ Restore ➪ File or Filegroups to

select the files or filegroups you wish to restore

Restoring with T-SQL code

Database backup is a regularly scheduled occurrence, so if SQL Server’s built-in Maintenance Plan

Wiz-ard isn’t to your liking, it makes sense to write some repeatable code to perform backups and set up

your own SQL Server Agent jobs

However, unless the backup plan is only a full backup, it’s difficult to know how many differential

back-ups or transaction-log backback-ups need to be restored; and because each backup file requires a separate

RESTOREcommand, it’s difficult to script the recovery effort beforehand without writing a lot of code

to examine themsdbtables and determine the restore sequence properly

The backupset table in the msdb database contains a row for each backup set You can

query this table to find information on all the successful backups.

TheRESTOREcommand will restore from a full, differential, or transaction-log backup:

RESTORE DATABASE (or LOG) DatabaseName

Optional-File or Filegroup or Page

FROM BackUpDevice

WITH

FILE = FileNumber,

PARTIAL,

NORECOVERY or RECOVERY or STANDBY = UnDoFileName,

REPLACE,

STOPAT datetime,

STOPATMARK = ‘markname’

STOPBEFOREMARK = ‘markname’

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To restore a full or differential backup, use theRESTORE DATABASEcommand; otherwise, use the

RESTORE LOGfor a transaction log To restore a specific file or filegroup, add its name after the

database name ThePARTIALoption specifies a partial restore that restores the primary filegroup and

any specified secondary filegroup(s)

A backup set often contains several backup instances For example, a backup set might consist of the

following:

1: Full backup 2: Differential backup

3, 4, 5, 6: Transaction-log backups 7: Differential backup

8, 9: Transaction-log backups TheWITH FILEoption specifies the backup to restore If it’s not included in the command, the first

backup instance is restored

If a password was created with the backup, the password is required to perform a restore from the

backup

Avoid using the password option, as this feature will be removed in a future release of SQL Server.

To restore one or more pages, usePAGE =‘file:page[, .n]’, wherePAGEindicates a list of one or

more files and pages,fileindicates the file ID containing the page to be restored,pageindicates the

page ID of the page to be restored in the file, andnindicates multiple pages can be specified

TheRECOVERY/NORECOVERYoption is vital to theRESTOREcommand Every time a SQL Server

starts, it automatically checks the transaction log, rolling back any uncommitted transactions and

completing any committed transactions This process is called recovery, and it’s a part of the ACID

properties of the database

Therefore, if the restore has theNORECOVERYoption, SQL Server restores the log without handling any

transactions Conversely,RECOVERYinstructs SQL Server to handle the transactions In the sequence of

the recovery operation, all the restores must have theNORECOVERYoption enabled except for the last

restore, which must have theRECOVERYoption enabled

Deciding betweenRECOVERYandNORECOVERYis one of the complications involved in trying to write

a script to handle any possible future recovery operation

TheSTANDBYoption allows the recovery effects to be undone

If the recovery operation includes a transaction-log restore, the recovery can stop before the end of the

transaction log The optionsSTOPATandSTOPATMARKwill leave the end of the transaction log

unre-stored TheSTOPATaccepts a time, and theSTOPATMARKrestores only to a transaction that was

cre-ated with a named mark TheSTOPBEFOREMARKoption restores everything up to the beginning of the

marked transaction

TheREPLACEoption creates the database and its related files even if another database already exists

with the same name

Chapter 26, ‘‘Creating DML Triggers,’’ details SQL Server transactions and how to create marked transactions.

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The following script demonstrates an example of a restore sequence that includes a full backup and two

transaction-log backups:

BackUp and recovery example

CREATE DATABASE Plan2Recover;

Result:

Command(s) completed successfully

Continuing:

USE Plan2Recover;

CREATE TABLE T1 (

PK INT Identity PRIMARY KEY,

Name VARCHAR(15)

);

Go

INSERT T1 VALUES (’Full’);

go

BACKUP DATABASE Plan2Recover

TO DISK = ‘e:\P2R.bak’

WITH

NAME = ‘P2R_Full’,

INIT;

Result:

(1 row(s) affected)

Processed 168 pages for database ‘Plan2Recover’, file ‘Plan2Recover’

on file 1

Processed 6 pages for database ‘Plan2Recover’, file ‘Plan2Recover_log’

on file 1

BACKUP DATABASE successfully processed 174 pages in 0.800 seconds

(1.690 MB/sec)

Continuing:

INSERT T1 VALUES (’Log 1’);

go

BACKUP Log Plan2Recover

WITH

NAME = ‘P2R_Log’;

Result:

(1 row(s) affected)

on file 2

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BACKUP LOG successfully processed 6 pages in 0.113 seconds (0.393 MB/sec)

Continuing:

INSERT T1 VALUES (’Log 2’);

go BACKUP Log Plan2Recover

WITH NAME = ‘P2R_Log’;

Result:

(1 row(s) affected) Processed 1 pages for database ‘Plan2Recover’, file ‘Plan2Recover_log’

on file 3

BACKUP LOG successfully processed 1 pages in 0.082 seconds (0.005 MB/sec)

Continuing:

SELECT * FROM T1;

Result:

-

(3 row(s) affected)

At this point the server is hit with a direct bolt of lightning and all drives are fried, with the exception

of the backup files The following recovery operation goes through the full backup and the two

transaction-log backups Notice theNORECOVERYandRECOVERYoptions:

NOW PERFORM THE RESTORE Use Master;

RESTORE DATABASE Plan2Recover FROM DISK = ‘e:\P2R.bak’

With FILE = 1, NORECOVERY;

Result:

on file 1

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RESTORE DATABASE successfully processed 174 pages in 0.168 seconds

(8.050 MB/sec)

Continuing:

RESTORE LOG Plan2Recover

FROM DISK = ‘e:\P2R.bak’

With FILE = 2, NORECOVERY;

Result:

on file 2

RESTORE LOG successfully processed 6 pages in 0.028 seconds

(1.586 MB/sec)

Continuing:

RESTORE LOG Plan2Recover

FROM DISK = ‘e:\P2R.bak’

With FILE = 3, RECOVERY;

Result:

on file 3

RESTORE LOG successfully processed 1 pages in 0.004 seconds

(0.122 MB/sec)

To test the recovery operation:

USE Plan2Recover;

Select * from T1;

Result:

-

(3 row(s) affected)

As this script shows, it is possible to recover using T-SQL, but in this case Management Studio beats

code as the best way to accomplish the task

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System Databases Recovery

So far, this chapter has dealt only with user databases, but the system databases are important to the

recovery operation as well Themasterdatabase contains key database and security information, and

theMSDBdatabase holds the schedules and jobs for SQL Server, as well as the backup history A

com-plete recovery plan must include the system databases

Master database

Themasterdatabase, by default, uses the simple recovery model Using only full backups for the

masterdatabase is OK; it’s not a transactional database

Backing up the master database

Themasterdatabase is backed up in the same manner as user databases Be sure to back up the

masterdatabase when doing any of the following:

■ Creating or deleting databases

■ Modifying security by adding logins or changing roles

■ Modifying any server or database-configuration options Because theMSDBdatabase holds a record of all backups, back up themasterdatabase and then the

MSDB

Recovering the master database

If themasterdatabase is corrupted or damaged, SQL Server won’t start Attempting to start SQL

Server will have no effect Attempting to connect to the instance with Management Studio will invoke a

warning that the server does not exist or that access is denied The only solution is to first rebuild the

masterdatabase using the command-line setup (as shown next), reapply any SQL Server updates, start

SQL Server in single-user mode, and restore themasterdatabase

1 Rebuild themasterdatabase using the following command-line setup:

setup /QUIET /ACTION=REBUILDDATABASE /INSTANCENAME="<instance name>"

/SQLSYSADMINACCOUNTS="<DomainName\UserName >" /SAPWD="<password>"

■ setup.exeis either from your original installation media or the ‘‘local’’setup.exeas found in the 100\Setup Bootstrap\Release directory

■ The/QUIETswitch suppresses all error messages

■ The/ACTION=REBUILDDATABASEswitch rebuilds all the system databases

■ The/INSTANCENAMEswitch specifies the name of your SQL Server named instance Use MSSQLServerfor ‘‘<instance_name>’’ for the default instance.

■ The/SQLSYSADMINACCOUNTSswitch corresponds to the currently logged in domain user running this rebuild process The user must be a member of the SQL Server instance’s sysadmin server role

■ The/SAPWDswitch is used to indicate a new SA password if you configured SQL Server for mixed authentication

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A new feature has been added to rebuilding the system databases The system databases

used for rebuilding the local system databases do not come from the original installation

media and are located locally in the \BINN\Templates folder, and setup.exe is located in the 100\Setup

Bootstrap \Release folder Also notice that the switches have changed compared to SQL Server 2005.

2 Run the following from the command prompt to start a default instance of SQL Server in

single-user mode:

sqlservr.exe -m

To start a named instance of SQL Server in single-user mode, run the following:

sqlservr.exe -m -s <instancename>

3 Reapply any SQL Server updates, service packs, and hotfixes that were previously applied to

the SQL Server

4 Restore themasterdatabase as you would a user database If amasterbackup is not

available, then recreate all missing entries for your user databases, logins, endpoints, and so

forth

If the masterdatabase is accessible, start SQL Server in single-user mode and then restore themaster

database as you would a user database

Rebuilding the master database rebuilds the msdb and model databases too, so after

rebuilding the databases restore the system databases ( master , msdb , model ) from the most

recent good backup.

Rebuilding the master database installs all system databases to their initial location If initially one or

more system databases were moved to a different location, then a similar move is required again now.

MSDB system database

Like themasterdatabase, themsdbdatabase, by default, uses the simple recovery model

Because themsdbdatabase contains information regarding SQL Server Agent jobs and schedules, as well

as the backup history, it should be backed up whenever you do the following:

■ Perform backups

■ Save SSIS packages

■ Create new SQL Server Agent jobs

■ Configure SQL Server Agent mail or operators

■ Configure replication

■ Schedule tasks

Themsdbdatabase is backed up in the same way that a user database is backed up

To restore themsdbdatabase, you do not need to put the server in single-user mode, as you do with

themasterdatabase However, it’s still not a normal restore, because without a currentmsdb,

Man-agement Studio is not aware of the backup history Therefore, themsdbbackup can’t be chosen as a

backup database but must be selected as a backup device

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