File recovery technology for SQL Server

SQL Server has two types of backup, one is to use backup database to back up the file, the other is to directly copy the database file MDF and log file LDF way. In this article, we will mainly introduce the latter's backup and recovery. (This article assumes that you are now proficient with Server Enterprise Manager and SQL Server Query Analyzer)

1. Normal backup and Recovery methods

Normally, to back up a database, first disconnect the database from the running Data server, or deactivate the entire database server, and then copy the files.

To remove a database command:

sp_detach_db database name

command to connect to a database:

sp_attach_db or sp_attach_single_file_db s_attach_db [@dbname =]′dbname′, [@filename1 =]′filename_n′[,... sp_attach_single_file_db [@dbname =]′dbname′, [@physname =]′physical_name′

Use this method to correctly restore SQL Sever 7.0 and SQL Server 2000 database files, which is important when backing up the MDF and LDF two files, the MDF file is the database data file, and the LDF is the database log file.

Example:

Suppose the database is test, its data file is Test_data.mdf, and the log file is test_log.ldf. Let's discuss how to back up and restore the database.

To remove a database:

sp_detach_db ' Test '

To connect to a database:

sp_attach_db ' test ', ' C:Program filesmicrosoft sql Servermssqldatatest_data.mdf ', ' C:Program FilesMicrosoft sql Servermssqldatatest_log.ldf ' sp_attach_single_file_db ' test ', ' C:Program filesmicrosoft SQL servermssqldatatest_ Data.mdf '

2, only the MDF file recovery technology

For a variety of reasons, if we had just backed up the MDF file, it would be a hassle to recover.

If your MDF file is generated by the current database, then it is a fluke that you may use sp_attach_db or sp_attach_single_file_db to recover the database, but you will receive a hint similar to the following:

Device activation error. The physical filename ' c:program filesmicrosoft SQL servermssqldatatest_log.ldf ' may be incorrect.

Created named ' C:Program FilesMicrosoft SQL servermssqldatatest_log. LDF ' new log file.

However, if your database files are replicated from other computers, unfortunately, perhaps the above approach will not work. You may receive an error message similar to the following:

Server: Message 1813, Level 16, State 2, line 1

Failed to open new database ' test '. The CREATE DATABASE will terminate.

Device activation error. Physical filename ' D:test_log. LDF ' may be wrong.

What should we do? The following example illustrates the recovery approach.

A, we use the default method to establish a database for recovery, such as test. Can be built in SQL Server Enterprise Manager.

B, stop the database server.

C, delete the log file test_log.ldf the database you just generated, overwriting the database data file you just generated with the database MDF file you want to restore test_data.mdf.

D, start the database server. You will see that the state of the database test is suspect. No action can be made on this database at this time.

E, the Setup database allows direct operating system tables. This action allows you to select the database server in SQL Server Enterprise Manager, right-click, select Properties, and select the Allow direct modifications to system directories on the server Settings page. You can also use the following statement to implement it.

Use master go sp_configure ' allow updates ', 1 go reconfigure with override go

F, set test to Emergency Repair mode

Update sysdatabases set status=-32768 where dbid=db_id (' test ')

You can see in SQL Server Enterprise Manager that the database is in "read-only suspect offline emergency mode" to see the tables in the database, but only the system tables.

G, perform a real restore operation below, rebuild the database log file

DBCC REBUILD_LOG (' Test ', ' C:Program filesmicrosoft SQL servermssqldatatest_log.ldf ')

During execution, if you encounter the following prompt information:

Server: Message 5030, Level 16, State 1, line 1

Failed to lock the database to perform the operation.

DBCC execution completed. If DBCC prints an error message, contact your system administrator.

Indicates that your other program is using the database, and if you have just opened the system table of the test library using SQL Server Enterprise Manager in step F, then quit SQL Server Enterprise Manager.

The prompt for completion should resemble the following:

Warning: Log of database ' Test ' has been rebuilt. The consistency of the transaction has been lost. DBCC CHECKDB should be run to verify physical consistency. You will have to reset the database options, and you may need to delete the extra log files.

DBCC execution completed. If DBCC prints an error message, contact your system administrator.

When you open the SQL Server Enterprise Manager, you will see that the state of the database is "for dbo use only." You can now access the user table inside the database.

H, verify database consistency (can be omitted)

DBCC CHECKDB (' test ')

The results of the general implementation are as follows:

CHECKDB found 0 allocation errors and 0 consistency errors (in the database ' test ').

DBCC execution completed. If DBCC prints an error message, contact your system administrator.

I, set the database to a normal state

sp_dboption ' test ', ' dbo use only ', ' false '

If nothing goes wrong, you can now use the restored database normally.

J, in the final step, we will restore the "allow direct modifications to the system directory" set in step e. Because the ordinary direct operating system table is a more dangerous thing. Of course, we can recover in SQL Server Enterprise Manager, or we can do this with the following statement.

sp_configure ' allow updates ', 0 go reconfigure with override go