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All technological notes.

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Recovery - Complete Recovery: Using Image Copy

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• Recovery - Complete Recovery: Using Image Copy
  • Fast Recovery using SWITCH command
    • Switch back to original location
    • Restoring Datafiles to a Nondefault Location Using SET NEWNAME
  • Applying Incremental backups to data file Image copies

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Fast Recovery using SWITCH command

• SWITCH command:

  • updates the names of the files in the RMAN repository, but the database does not rename the files at the operating system level.

    • Update the file names for a database, tablespace, or data file to the latest image copies available for the specified files
    • Update the file names for data files and temp files for which you have issued a SET NEWNAME command

• Prerequisites:

  • RMAN must be connected to a target database.
  • When switching tablespaces, data files, or temp files, the files must be offline.
  • When switching the whole database, the database must not be open.

• Steps

  1. Take the data file offline.
  2. Usethe SWITCH TO ... COPY command to point to the image copy of the files.
  3. Recover the data files.
  4. Bring the data files online.
     • At this point, the database is usable, and the data files are recovered.

SWITCH DATAFILE 'filename' TO COPY;

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Switch back to original location

• Steps to put the data files back into their original location: 注意, 该步骤不同于上一节

  1. Use the BACKUP AS COPY command to create an image copy of the data files in the original location.
  2. Take the data files offline.
  3. Use the SWITCH TO COPY command to switch to the copy you made in step 1
  4. Recover the data files.
  5. Bring the data files online.

• 与上一节区别仅仅在于, 为保证转换后的文件还在原有路径, 将映像备份的保存在原有路径中. 则恢复时仅需将不工作的数据文件转换到原有路径的映像备份即可.

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Restoring Datafiles to a Nondefault Location Using SET NEWNAME

• If you cannot restore data files to their default locations, then you must update the control file to reflect the new locations of the data files. 当无法使用默认路径恢复数据文件时, 必须更新 cf

• SET NEWNAME command:

  • to specify the new file name
  • equivalent to using the SQL statement ALTER DATABASE RENAME FILE, to update the names of the data files in the control file.
  • Afterward, use SWITCH DATAFILE ALL command to update the control file to reflect the new names for all data files.
  • used only inside a RUN block

• Example:

RUN
{
    ALLOCATE CHANNEL devl DEVICE TYPE DISK;
    ALLOCATE CHANNEL dev2 DEVICE TYPE sbt;
    SQL "ALRER TABLESPACE users OFFLINE IMMEDIATE";
    SET NEWNAME FOR DATAFILE '/diskl/oradata/prod/users01l.dbf"'
                        TO '/disk2/users0l.dbf';
    RESTORE TABLESPACE users;
    SWITCH DATAFILE ALL;
    RECOVER TABLESPACE users;
    SQL "ALTER TABLESPACE users ONLINE";
}

• Instead of individual names, a more efficient way is to use the SET NEWNAME clause to specify the default name format for all data files in a named tablespace and all data files in the database.

  1. SET NEWNAME FOR DATAFILE and SET NEWNAME FOR TEMPFILE
  2. SET NEWNAME FOR TABLESPACE
  3. SET NEWNAME FOR DATABASE
  • The default name is used for DUPLICATE, RESTORE, and SWITCH commands in the RUN block.该默认名将被用于同一个代码中

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Applying Incremental backups to data file Image copies

• To recover Image Copies + incremental backups:

  • Image copies are updated with all changes up to the incremental backup SCN.
  • reduces the time required for media recovery.
  • no need to perform an image copy after the incremental restoration.

• Applying incremental backups to data file image copies:

  • roll forward (recover) the image copy to the specified point in time
    • update the image copy with all changes up through the SCN at which the incremental backup was taken.
  • the resulting updated data file just as a full image copy taken at that SCN, without the overhead of performing a full image copy of the database every day.

• Benefits:

  • reduce the time required for media recovery (using archive logs)减少恢复时间
    • because you need to apply archive logs only since the last incremental backup.
  • do not need to perform a full image copy after the incremental restoration.无需全备份

• Characteristics:

  • If the recovery process fails during the application of the incremental backup file, you simply restart the recovery process. 如果恢复操作出错, 仅需重启

    • RMAN automatically determines the required incremental backup files to apply, from before the image data file copy until the time at which you want to stop the recovery process. 自动适用自增备份

  • If there is more than one version of an image copy recorded in the RMAN catalog 如果有多个备份

    • RMAN automatically uses the latest version of the image copy. 自动适用最后一个

• RMAN reports an error if it cannot merge an incremental backup file with an image copy.

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Example: continuously updated image copies(略, 查看 strategy)

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