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What happen when Tablespace begin in backup mode. [message #62565] Thu, 29 July 2004 04:38 Go to next message
BhavinShah
Messages: 105
Registered: February 2004
Senior Member
Hi..
friends,

I wanted to know exactly what happen in database when we issue command.
alter tablespace name begin backup;

Thax..
Re: What happen when Tablespace begin in backup mode. [message #62568 is a reply to message #62565] Thu, 29 July 2004 07:20 Go to previous messageGo to next message
Frank Naude
Messages: 4580
Registered: April 1998
Senior Member
Hi,

The following will happen when you do a BEGIN BACKUP on a tablespace:

1) Oracle will stop updating the tablespace's file headers; and

2) Oracle will write more data to the redo log files (write complete blocks instead of deltas); and

3) Oracle will continue to write COMMITed changes to the tablespace's data files; and

3) Oracle will wait for you to backup the datafiles and issue an END BACKUP command :-)

Best regards.

Frank
Really Oracle write data to logfile. [message #62574 is a reply to message #62568] Thu, 29 July 2004 22:55 Go to previous messageGo to next message
BhavinShah
Messages: 105
Registered: February 2004
Senior Member
Hi,

Frank

Is it really oracle write data to logfile when tablespace begin backup mode . if i have not enough space in redo log file then what happen??

bye..
bhavin
Re: Really Oracle write data to logfile. [message #62577 is a reply to message #62574] Fri, 30 July 2004 05:15 Go to previous messageGo to next message
Frank Naude
Messages: 4580
Registered: April 1998
Senior Member
Hi,

Yes, that is correct!

The redo log files will be archived as usual. If your archive destination gets full, your database will hang until the directory is cleared (backup/ move archived log files). Again, this is expected and documented behaviour. To prevent any problems, don't backup your database if you have too many users working!

Best regards.

Frank
Re: What happen when Tablespace begin in backup mode. [message #62614 is a reply to message #62568] Tue, 03 August 2004 01:40 Go to previous message
Satheesh Babu.S
Messages: 35
Registered: July 2004
Member
I want to elaborate point 2 and 3 of frank,
"2) Oracle will write more data to the redo log files (write complete blocks instead of deltas); and"

In order to avoid split block problem oracle write whole block into to redo log file. When a block is changed first time in the db cache, the whole block will get into redo log file. If any subsequent changes happening to this block later will sent only the deltas to redo log file. Incase if this block is flushed to datafile and brought it back by other processes, then first changes to this block will again move whole block to redo log and subsequent change.
So that's the reason begin backup has to be done when there is relatively less work in the db.

"Oracle will continue to write COMMITed changes to the tablespace's data files; and"

Not only committed data, even uncommited datas will get into datafile. This is true even for redo log file.

Thanks and Regards,
Satheesh Babu.S
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