| begin backup mode [message #241791] |
Wed, 30 May 2007 11:28  |
bksrisai
Messages: 30
Registered: May 2007
Location: hyderabad
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Member |
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hi, when i am taking hot backup, i am issuing alter tablespace .. begin backup and i am copying datafiles mean while i am doing transactions and atlast i am keeping the tablespaces in end backup mode, my question is what's happening when i keep the tablespace in begin backup mode
thanks in advance..
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| Re: begin backup mode [message #241807 is a reply to message #241791] |
Wed, 30 May 2007 11:49  |
hardeys
Messages: 4
Registered: May 2007
Location: India
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Junior Member |
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Hi,
As soon as you put the tablespace in Backup Mode, nothing is written to tablespace datafiles as long as it is Backup mode. All the transactions that need to be posted these files are recorded in redo log files. When the tablespace is in normal mode, the changes from redo log are written back to datafiles. This is reason why System generate more redo when a tablespace is in Backup mode and it is because of this reason we don't put all the tablespace in backup mode at the same time.
Hope it helps you.
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| Re: begin backup mode [message #241808 is a reply to message #241791] |
Wed, 30 May 2007 11:49 |
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Michel Cadot
Messages: 68651
Registered: March 2007
Location: Nanterre, France, http://...
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Senior Member
Account Moderator |
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Have a look at Backup and Recovery Concepts, Chapter 2 "Backup Principles", section Backups of Online Tablespaces and Datafiles
Especially:
| Quote: | You must first place the online tablespace in backup mode with the ALTER TABLESPACE BEGIN BACKUP statement. As a result, Oracle stops recording checkpoints to the tablespace's datafiles.
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| Quote: | After an online backup is completed, Oracle advances the file header to the current database checkpoint, but only after you run the ALTER TABLESPACE ... END BACKUP or ALTER DATABASE END BACKUP statement to take the tablespace out of backup mode.
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| Quote: | When you restore a datafile from an operating system backup, the datafile header has a record of the most recent datafile checkpoint that occurred before the online tablespace backup, not any that occurred during it. As a result, Oracle asks for the appropriate set of redo log files to apply should recovery be needed.
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During backup mode, Oracle generates more redo logs as each first modification in a block leads to the copy of the whole block in redo file. So the longest is the backup the more blocks of the tablespace may be copied into redo logs.
Regards
Michel
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