online backup

online backup

Post by Alvi » Sun, 31 Dec 1899 09:00:00



hi,all
when I do online backup,after the command
alter tablespace abc begin backup;
if I modify data in the tablespace abc,what will happen??
ORACLE will store modified data in somewhere else?? or .....

THx

Alvin Huang

 
 
 

online backup

Post by yong.. » Sun, 31 Dec 1899 09:00:00




Quote:> hi,all
> when I do online backup,after the command
> alter tablespace abc begin backup;
> if I modify data in the tablespace abc,what will happen??
> ORACLE will store modified data in somewhere else?? or .....

> THx

> Alvin Huang

Data will be written to online redo log files.

--
Yong Huang


(http://www.stormloader.com/yonghuang/)

Sent via Deja.com http://www.deja.com/
Before you buy.

 
 
 

online backup

Post by Andreas Stepha » Sun, 31 Dec 1899 09:00:00


Hi Alvin,

after the "begin backup" command, oracle will prevent the headers of the
data file to be written to.
Data blocks are (!!) written to the files (and of course to the redo-log
files with some additional info during backup time). This is done to
ensure a definite point for recovery to start. If you ever have to
restore a datafile, Oracle will check the header of the datafile against
the information in the control files and apply all redo logfiles
(archived and online) which are older than the information in the
controlfile but younger than the information in the datafile header.
The blocks are written to the datafile, to ensure that changes are in
the datafile.

If you switch from begin backup to end backup, headers are free again
and the next checkpoint will overwrite the old header and from now on
the modified rows in the datafile(s) are valid. Subsequent shutdown /
startup sequences will not apply any redologs. If the checkpoint has not
already run before the database goes down, then a recovery will occur at
startup time.

Hope this helps.
Andy

Alvin schrieb:

Quote:> hi,all
> when I do online backup,after the command
> alter tablespace abc begin backup;
> if I modify data in the tablespace abc,what will happen??
> ORACLE will store modified data in somewhere else?? or .....

> THx

> Alvin Huang

 
 
 

1. Online backup: Backup online redologs?

Kevin Loney's Oracle 8 DBA handbook mentions the following 3-step
process for a online/hot backup:

1. Backup each tablespace by putting it in backup mode
2. Backup the archived redologs (and optionally delete them to save
space)
3. Backup the controlfile using ALTER DATABASE BACKUP CONTROLFILE

Why is there no mention of the online redologs? During BEGIN BACKUP,
arent the changed blocks written to the online redologs (in addition
to the datafiles themselves)? So, if my entire backup is over before
the online logs cycle, my online backup will be missing the changes
generated during the backup since they are present only in the online
redologs, right? What am I missing?

And if the online redologs should indeed be backed up, shouldnt there
be a BEGIN BACKUP for them as well since they are in a state of flux?

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