Catalog and Nocatalog differences in Oracle Rman backup

Nocatalog Way: Use control file as the catalog, each backup to the control files to write a lot of backup information, control files there will be more and more backup information, that is, Rman backup information written in the local control file.

Catalog Mode: You must first create a directory backup database (catalog, also known as the Knowledge Base), establish a recovery directory, that is, the database backup information is written to the recovery directory.

When backing up an Oracle database via Rman nocatalog, Oracle uses Controlfile to store backup information for Rman. Therefore, when backing up a database using Rman Nocatalog, be sure to remember to back up Controlfile.

Initialization parameters Control_file__record_keep_time Set the backup information to save time, and automatically clear the previous backup information to the specified time:

Sql> alter SYSEM set control_file_record_keep_time=7 scope=spfile;

Note:
When using Rman nocatalog recovery, the database is at least "mount" state, the control file must be loaded first, or Rman cannot find the backup information for the record. The prerequisite for Oracle startup mount is that control must exist. Therefore, you must restore the controlfile before recovering datafile. When using the Rman catalog mode, you can start Nomount and restore Controlfile, but when you use Rman Nocatalog, you must first restore the Controlfile in file mode.

The following steps are compared to the recovery of Rman Nocatalog and Rman Catalog in order to establish the correct backup strategy (the following recovery is a backup in the online state):

Rman nocatalog Recovery:
1) Establish Oracle Runtime environment (including init or SP files)
2) file mode restore Controlfile to the location specified in the Init file (or start to Nomount, restore Controlfile from Autobackup in Rman)
3) Startup Mount
4) Rman,restore Datafile,recover datafile
5) ALTER DATABASE open Resetlogs

Rman Catalog Recovery:
1) Establish Oracle Runtime environment (including init or SP files)
2) Rman, restore Controfile
3) ALTER DATABASE mount
4) Rman, restore Datafile,recover datafile
5) ALTER DATABASE open Resetlogs

As you can see, the Rman Nocatalog backup must be backed up by file Controlfile.

In addition, because Nocatalog uses Controlfile to store backup information, it is recommended to increase the Control_file_record_keep_time value in the ORACLE parameter file (by default, 7 days), which is $oracle_home/dbs /initsid.ora (9i may also be in SPFile, can only be changed by Oracle statements).

The recovery catalog (that is, catalog mode) supports the following commands
{create| upgrade| DROP} CATALOG
{create| delete| replace| PRINT} SCRIPT.
LIST incarnation
REGISTER DATABASE
Report SCHEMA at time 
RESET database 
RESYNC catalog 

1, RESYNC command  
Resync can synchronize the information between the database and the recovery directory, and in practice, Rman can generally automatically synchronize.  
to synchronize  
· Changes in the physical structure of the database  
• Increase or change the size of the data file • tablespace deletion  
• Create and delete rollback segments • 10 archived logs per generation  

2, Reset command  
after the target database resetlogs, you need to reset the recovery directory. The reset command is used to reset the recovery directory.