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Home -> Community -> Mailing Lists -> Oracle-L -> RE: RMAN: What blocks are backed up with a full backup?
I apologize, I shouldn't be trying to teach the master.
-----Original Message-----
Sent: Friday, April 04, 2003 12:09 PM
To: Multiple recipients of list ORACLE-L
This is accurate and far more correct than my quickly written statement was. I actually say this almost word for word in the book. This is why even a table truncate will not reduce RMAN space usage. Sorry, I'll endevor in the future to be more susinct! :-)
RF
-----Original Message-----
To: Multiple recipients of list ORACLE-L
Sent: 4/4/2003 10:13 AM
What it doesn't write are the blocks that are not allocated to any
extent. RMAN doesn't go into the logical structures, like tables and
indexes,
it looks into the tablespace header and reads the information from the
bitmap information there. It cannot go into tables/indexes because it
should also work when the database is only mounted and not opened, which
genrally means that data dictionary is not accessible. Empty blocks
are blocks that don't have any rows in them but are allocated to an
extent. New or unallocated blocks are blocks that have been initialized
when the datafile was allocated to the tablespace but have not been
assigned
to any object (table, index, materialized view, cluster, partition or
alike)
-----Original Message-----
Sent: Thursday, April 03, 2003 4:24 PM
To: Multiple recipients of list ORACLE-L
Actually this is how RMAN works. It writes all blocks up to the HWM of a
given table,
even empty ones. So, if your HWM is artifically high, you will encounter
backups
that are larger than they need to be.
Oracle9i RMAN Backup and Recovery.... On bookshelves now!
RF
-----Original Message-----
To: Multiple recipients of list ORACLE-L
Sent: 4/3/2003 11:19 AM
Keith
Here is my understanding (don't rely on this one). When Oracle
allocates
tablespace, the disk blocks are cleared. My interpretation is that when
RMAN
encounters a clear block, it doesn't write it to the backup piece. I
don't
think it spends a lot of time trying to figure out above HWM and such.
Dennis Williams
DBA, 40%OCP, 100% DBA
Lifetouch, Inc.
dwilliams_at_lifetouch.com
-----Original Message-----
Sent: Thursday, April 03, 2003 10:44 AM
To: Multiple recipients of list ORACLE-L
Our RMAN backup is backing up much more than the actual data blocks when
doing a full backup. I know that it backs up all blocks that have "ever
been
used", but I'm trying to figure out exactly what that means. My first
thought was that it backs up all blocks below the HWM, but I analyzed
the
tables and that is not the case.
Sometimes it backs up more blocks than exist below the HWM for the
tables
and sometimes it backs up fewer blocks than those below the HWM.
We are doing this to determine what we can do to reduce the size of the backup.
Anyone have an idea how this works?
Keith
--
Please see the official ORACLE-L FAQ: http://www.orafaq.net
--
Author: DENNIS WILLIAMS
INET: DWILLIAMS_at_LIFETOUCH.COM
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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 Fri Apr 04 2003 - 12:03:39 CST
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