Oracle database backup and recovery

Oracle database backup and recovery

Oracle database backup and recovery

The ORACLE tutorial is backup and recovery of the Oracle database. ---- When we use a database, we always hope that the content of the database is reliable and correct. However, due to computer system faults (including machine faults, media faults, and misoperations ), databases may also be damaged, so it is imperative to restore data as soon as possible. If the database is backed up at ordinary times, it is easy to restore data. This shows how important it is to back up a database. Let's take ORACLE7 as an example to describe how to back up and restore the database. ORACLE databases have three standard backup methods: EXPORT/IMPORT, cold backup, and hot backup. Exporting backup is a logical backup, while cold backup and hot backup are physical backup.

---- 1. Export/Import (Export/Import)

---- Export can be used to extract data from the database, and Import can be used to send the extracted data back to the Oracle database.

---- 1. Simple Export of data (Export) and Import of data (Import)

---- Oracle supports three types of output:

---- (1) Export the data of the specified table in the table (T) mode.

---- (2) user mode (U mode): exports all objects and data of the specified user.

---- (3) Full database (Full): export all objects in the database.

---- The data Export process is the inverse process of the data Import (Export). Their data flows are different.

---- 2. incremental Export/Import

---- Incremental export is a common data backup method. It can only be implemented for the entire database and must be exported as a SYSTEM. During this export, the system does not require any answers. The default export file name is export. dmp. If you do not want your output file to be named export. dmp, you must specify the file name to use in the command line.

---- Incremental export includes three types:

---- (1) "Complete" incremental Export (Complete)

---- Back up the entire database, for example:

---- $ Exp system/manager inctype = complete file = 990702.dmp

---- (2) incremental Export

---- Back up the data changed after the last backup. For example:

---- $ Exp system/manager inctype = incremental file = 990702.dmp

---- (3) Cumulative)

---- The accumulative export method only exports the changed information in the database after the last "full" export. For example:

---- $ Exp system/manager inctype = cumulative file = 990702.dmp

---- The database administrator can schedule a backup schedule and export data in three different ways to achieve reasonable and efficient completion.

---- For example, the database backup task can be arranged as follows:

---- Monday: full export ()

---- Tuesday: Incremental Export (B)

---- Wednesday: Incremental Export (C)

---- Thursday: Incremental Export (D)

---- Friday: accumulative Export (E)

---- Saturday: Incremental Export (F)

---- Sunday: Incremental Export (G)

---- If the database is accidentally damaged on Sunday, the database administrator can follow these steps to restore the database:

---- Step 1: Use the create database Command to regenerate the DATABASE structure;

---- Step 2: create an additional return segment that is large enough.

---- Step 3: import A in full Increments:

---- $ Imp system./manager inctype = rectore full = y file =

---- Step 4: Accumulative incremental import E:

---- $ Imp system/manager inctype = rectore full = y file = E

---- Step 5: import the latest incremental F:

---- $ Imp system/manager inctype = restore full = y file = F

---- II. Cold backup

---- Cold backup occurs when the database is shut down normally. When the database is shut down normally, it will provide us with a complete database. Cold backup is a way to copy key files to another location. Cold backup is the fastest and safest way to back up Oracle information. Advantages of cold backup:

---- 1. It is a very fast backup method (just copy files)

---- 2. Easy to archive (simple copy)

---- 3. Easy to restore to a certain point in time (you only need to copy the file back)

---- 4. It can be combined with the archiving method to restore the database to the "latest State.

---- 5. Low maintenance and high security.

---- However, cold backup also has the following shortcomings:

---- 1. When used separately, only the restoration at a certain time point can be provided.

---- 2. During the whole backup process, the database must be backed up instead of other work. That is to say, in the cold backup process, the database must be closed.

---- 3. If the disk space is limited, it can only be copied to tape and other external storage devices, and the speed will be very slow.

---- 4. data cannot be restored by table or by user.

---- If possible (mainly for efficiency), back up the information to the disk and start the database (allowing the user to work) and copy the backed up information to the tape (the database can work at the same time ). Files that must be copied in cold backup include:

---- 1. All data files

---- 2. All control files

---- 3. All online redo log files

---- 4. Init. ora file (optional ).

---- It is worth noting that cold backup must be performed when the database is closed. When the database is turned on, the execution of database file system backup is invalid.

---- The following is a complete example of cold backup:

---- (1) Close the database $ sqldba lmode = y

---- SQLDBA> connect internal;

---- SQLDBA> shutdown normal;

---- (2) use the copy command to back up all the time files, redo log files, control files, and initialize parameter files

---- SQLDBA>! Cp <file> <backup directory>

---- (3) restart the Oracle database

---- $ Sqldba lmode = y

---- SQLDBA> connect internal;

---- SQLDBA> startup;

---- III. Hot Backup

---- Hot Backup uses archivelog mode to back up data when the database is running. Therefore, if you have a cold backup file last night and a hot backup file today, you can use this data to restore more information when a problem occurs. Hot Backup requires that the database be operated in Archivelog mode and requires a large amount of archive space. Once the database is running in the archivelog state, you can back up the database. The Hot Backup command file consists of three parts:

---- 1. Data Files are backed up in one tablespace and one tablespace.

---- (1) set the tablespace to the backup status

---- (2) back up the data files in the tablespace

---- (3) restore the tablespace to normal state

---- 2. Back up the archive log file.

---- (1) temporarily stop the archiving process

---- (2) files in the target directory of archive redo log under log

---- (3) restart the archive Process

---- (4) back up the archived redo log file

---- 3. Use the alter database backup controlfile command to back up and copy files

---- Advantages of Hot Backup:

---- 1. Backup can be performed at the tablespace or data file level, with a short backup time.

---- 2. The database is still available during Backup.

---- 3. It can be restored in seconds (to a specific point in time ).

---- 4. Restore almost all database entities.

---- 5. Recovery is fast, and recovery is usually performed when the database is still working.

---- Hot backup is insufficient:

---- 1. No error is allowed; otherwise, the consequences are serious.

---- 2. If the Hot Backup fails, the result cannot be used for restoration at the time point.

---- 3. Because it is difficult to maintain, you must be careful not to "end with failure ".

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