Re: RMAN backup - basic Qs

does this make RMAN hot backups faster or slower than when backing up file in backup mode?

Rajesh.Rao_at_jpmchase.com wrote:

> 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 ?
> >
> > --
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> > --
> > Author: VIVEK_SHARMA
> > INET: VIVEK_SHARMA_at_infosys.com
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
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> Author:
> INET: Rajesh.Rao_at_jpmchase.com
>
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--
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Oracle DBA
Philippine Stock Exchange, Inc.

"If you don't risk anything, you risk even more."


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