RE: RMAN backup - basic Qs

To better answer the original question, my understanding of this difference is as under:

Why do you put the tablespace in backup mode during normal hot backups without RMAN? This is to avoid backing up "split blocks". Say, you have a database with a block size of 16K. And that a block is in the process of being backed up, with reads happening in chunks of say, 512 bytes. Assume a user transaction updates this block while the backup is in progress. This could result in an inconsistent version of the block being backed up, or what is called as "split blocks". Putting a tablespace in backup mode, is primarily, a flag which tells Oracle to copy the entire block into the redo stream, and not just the changed vectors or deltas, which it would have done otherwise. This is so that, in case of recovery, the entire block can be read from the redo stream, and applied. Hence, this results in an increase in the redo size during normal hot backups.

RMAN however, does not place the tablespaces in hot backup mode. They use the same read consistency mechanism used by the SQL statements. Hence, no excessive redo is generated.

Hope this helps.

Raj

----Original Message-----
Sent: Thursday, January 16, 2003 1:54 PM To: Multiple recipients of list ORACLE-L

Rman uses the same construct to get the right data in a hot backup as sqlplus, the SCN of the database. It reduces excess redo because you don't have to put the datafile in backup mode with a begin backup and take it out

with and end backup.

HTH,
Ruth
----- Original Message -----
To: "Multiple recipients of list ORACLE-L" <ORACLE-L_at_fatcity.com> Sent: Thursday, January 16, 2003 12:35 PM

>
> Is Excessive Redo Generated during RMAN OPEN Database backup using backup

sets as happens in case of HOT Backup ?
>
> If NOT , Why ?
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author: VIVEK_SHARMA
> INET: VIVEK_SHARMA_at_infosys.com

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: 
  INET: Rajesh.Rao_at_jpmchase.com

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