Shulou(Shulou.com)06/02 Report--

Media recovery and instance recovery

The following is all personal understanding and does not represent the official meaning of oracle. Please think about it carefully. Please correct any mistakes. Analysis of the personal meaning of two nouns: what is media recovery: what is media, media is a data file. Media recovery is the recovery of data files. What instance recovery: what is an instance, an instance is memory and processes. That is, the database reads the data that needs to be recovered in redo into memory. The data file may not change. Of course, it is also possible to change.

1. The system shuts down normally:

System scn=datafile scn=start scn=stop scn

1) system scn=datafile scn=start scn, no media recovery required

2) stopscn not null, no instance recovery required

2. Abnormal system shutdown:

System scn=datafile scn=start scn,stop scn null

1) system scn=datafile scn=start scn, no media recovery required

2) stopscn null, instance recovery is required (to put it bluntly, it is possible to read the online log and roll forward)

3. Old data files

System scn=datafile scn > start scn,stop scn null/notnull

1) system scn=datafile scn > start scn, the media needs to be restored to system scn=datafile scn=start scn (backup control files are most likely used. Or the control file is up-to-date, but the data file is restored from a full backup.

2) stopscn null, which requires instance recovery, while not null does not require instance recovery.

4. Backup control files

System scn=datafile scn=start scn, the media needs to be restored to system scn=datafile scn=start scn=redolog scn (maximum SCN of current log), stop scn not null

2) stopscn not null does not need instance recovery

6. Reconstruct the datafile Checkpoint in the resetlogs control file control file from each data file header.

System scn > = datafile scn=start scn,stop scn not null/null

1) system scn > = datafile scn=start scn, you need to use using backup controlfile media to restore to system scn=datafile scn=start scn (maximum SCN of current log), stop scn not null

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