Comparison between cold backup and Hot Backup

I. 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. This article describes how to copy key files to another location during cold backup. The fastest and safest way to back up Oracle information during cold backup. Advantages of cold backup:

1. It is a very fast backup method (just copy files)
2. Easy archiving (simple copy)
3. easy recovery 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 in the "best state.
5. Low maintenance and high security.

However, cold backup also has the following shortcomings:

1. When used separately, only recovery 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, start the database (allowing the user to work), and copy the backup information to the tape, the database can also work ). 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) shut down the database
Sqlplus/nolog
SQL> connect/As sysdba
SQL> shutdown normal;

(2) Use the Copy command to back up all the time files, redo log files, control files, and initialize parameter files.
SQL> CP

(3) restart the Oracle database
SQL> startup

Ii. Hot Backup

Hot Backup is used to back up the database in archivelog mode 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. Backup of one tablespace and one tablespace in a data file.

(1) set the tablespace to the backup state.
(2) back up the data files in the tablespace
(3) restore the tablespace to the normal state.

2. Back up archive log files

(1) temporarily stop the archiving process
(2) files in the archive Rede log target directory under Log
(3) restart the archive Process
(4) back up the archived redo log file

3. Use the alter database bachup controlfile command to back up and control files. The advantages of Hot Backup are:

1. Data can be backed up at the tablespace or database file level. The backup time is short.
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. In most cases, apsaradb recovers when it 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 a time point.
3. Because it is difficult to maintain, we must be extremely careful and do not agree to "end with failure ".