All,
The primary reason why RMAN does not generate
excessive redo is because because it does not put the
tablespace in "hot backup mode". Thus any blocks
belonging to a given tablespace that are modified
before the END BACKUP command is processed, do not
require block-level before and after images. Hence the
reduction in redo generation.
So how does RMAN backup without "hot backups"?
RMAN is aware of the format of an Oracle datafile, and
reads datafiles for the backup in DB_BLOCK_SIZE
chunks. This is not the case with most OS utilities
(tar, cpio, cp, dd etc.), which read files in 512-byte
OS blocksize chunks.
As a result, the issue of a fractured block (for which
block-level before/after images are taken) on the
destination where the backup is done, does not come
into play in RMAN.
Hope that helps,
Gaja
- "Goulet, Dick" <DGoulet_at_vicr.com> wrote:
> 1: RMAN does not generate excessive redo because it
> does not use the 'alter tablespace ... begin backup'
> command. It instead coordinates with dbwr, somehow,
> to be sure it is getting a consistent view of the
> tablespace.
>
> 2: The concept of an incremental backup is that you
> only backup the database blocks that have changed
> since the last incremental of the same or higher
> level. Somehow the date that the block changed is
> being managed, probably in the header somewhere.
>
> 3: If your reading a block for backup purposes, it's
> pretty easy to checksum it and compare with what's
> in the header just like the Oracle kernel does.
>
> 4: I've tried before with OmniBack and it's fairly
> simple. You only have to relink Oracle including a
> MML library file. The package you want to integrate
> with should have instructions.
>
> Dick Goulet
>
> -----Original Message-----
> Sent: Tuesday, April 01, 2003 10:19 AM
> To: Multiple recipients of list ORACLE-L
>
>
>
> Qs.1 Why is NO excessive Redo Generated wsing RMAN
> Backups unlike HOT Backups
> when taking backup of an OPEN Database which is
> undergoing User Transactions ?
> (Or am i mistaken ?)
>
> Qs.2 How does RMAN manage Incremental Database
> Backups ? What is the Concept behing it ?
>
> Qs.3 How does RMAN Check for Block Corruption while
> taking backup ?
>
> Qs.4 Is it easy to integrate 3rd part tools like
> Legato etc with RMAN for enabling taking
> of backups onto backup devices OR does it need an
> extensive setup ?
>
>
> --
> Please see the official ORACLE-L FAQ:
> http://www.orafaq.net
> --
> Author: VIVEK_SHARMA
> INET: VIVEK_SHARMA_at_infosys.com
>
> Fat City Network Services -- 858-538-5051
> http://www.fatcity.com
> San Diego, California -- Mailing list and web
> hosting services
>
> To REMOVE yourself from this mailing list, send an
> E-Mail message
> to: ListGuru_at_fatcity.com (note EXACT spelling of
> 'ListGuru') and in
> the message BODY, include a line containing: UNSUB
> ORACLE-L
> (or the name of mailing list you want to be removed
> from). You may
> also send the HELP command for other information
> (like subscribing).
>
> --
> Please see the official ORACLE-L FAQ:
> http://www.orafaq.net
> --
> Author: Goulet, Dick
> INET: DGoulet_at_vicr.com
>
> Fat City Network Services -- 858-538-5051
> http://www.fatcity.com
> San Diego, California -- Mailing list and web
> hosting services
>
> To REMOVE yourself from this mailing list, send an
> E-Mail message
> to: ListGuru_at_fatcity.com (note EXACT spelling of
> 'ListGuru') and in
> the message BODY, include a line containing: UNSUB
> ORACLE-L
> (or the name of mailing list you want to be removed
> from). You may
> also send the HELP command for other information
> (like subscribing).
>
Do you Yahoo!?
Yahoo! Tax Center - File online, calculators, forms, and more
http://platinum.yahoo.com
--
Please see the official ORACLE-L FAQ: http://www.orafaq.net
--
Author: Gaja Krishna Vaidyanatha
INET: oraperfman_at_yahoo.com
Fat City Network Services -- 858-538-5051 http://www.fatcity.com
San Diego, California -- Mailing list and web hosting services
---------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from). You may
also send the HELP command for other information (like subscribing).
Received on Tue Apr 01 2003 - 14:43:48 CST
