When we r taking hot backup(begin backup - end backup) the datafile heder associated with the datafiles in the corresponding tablespace is frozen.So Oracle will stop updating the datafile header but will continue to write data into datafiles.In backup oracle will generate more redos this is beacause oracle will write out complete changed blocks to the redo log files.

The two things will happen when the tablespace in backup mode

1.) The datafile header associated with the tablespace in the backup up mode will be in frozen state.So it stops updating the datafile header but it continually writes into the datafile.

2.) More redos are generated.This is because oracle will write all the changed blocks into the redo log.Normally only the changes are logged into the redo logs.

regards

Noyal

Hi

Everyone ..Answer given by all others are right and i am just adding a brief to it. actually what happens in backend when a tablespace is put up in backup mode is that the all datafile belonging the tablespace gets their checkpoint frozen. which means that next time the recovery should start after the checkpoint anything after the checkpoint is roll backward or roll forward to maintain consistency. At the same time database writter process writes to the datafile all the data blocks and the same data blocks are written to redo log files this is because the oracle block size and OS block sizes differs which results in fractured block to be copied by the OS utilities and for that reason when the file backuped up by hot backup required recovery and any fractured blocks are found out they are replaced by the actual block from archived log which are copy of redo logs.RMAN doesn't requires the tablespace to be put in the backup mode because oracle understands the block size and skips the block if a process is making change to it at the time of the backup.when you put the tablespace end backup the checkpoint is released and marked wih current checkpoint No and in this way oracle maintains consistency in the database.

Regards

Ritesh Raj Singh

Database Administration Team

ICICI Ltd

ICICI Corporate House

Mahalakshmi Mumbai

09322070038

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