RE: RMAN: What blocks are backed up with a full backup?

Yes, it would be good to read the bitmap. But I doubt if RMAN changes its behaviour depending on whether the Tablespace does or does not have ASSM -- the behaviour has to be consistent regardless of how you define storage parameters.
[in any case, again, it has to read the logical attributes of a logical entity -- a Tablespace, which it might not do].

Hemant

• Freeman Robert - IL <FREEMANR_at_tusc.com> wrote:

> But it does make sense that when ASSM is in use that RMAN would read
> the
> bitmap,
> doesn't it. Something for me to ask the Oracle RMAN folks.
>
> RF
>
> Robert G. Freeman
> Technical Management Consultant
> TUSC - The Oracle Experts www.tusc.com
> 904.708.5076 Cell (It's everywhere that I am!)
> Author of several books you can find on Amazon.com!
>
>
> -----Original Message-----
> Sent: Sunday, April 06, 2003 10:44 AM
> To: Multiple recipients of list ORACLE-L
>
>
>
> I partially agree with Mladen.
>
> RMAN definitely doesn't identify Table HWMs -- it doesn't know
> logical
> structures such as Tables and Segments and Tablespaces [although it
> can assist you in Tablespace Recovery when it reads the Data
> Dictionary].
> RMAN knows physical structures such as DataFiles, RedoLog Files and
> ControlFiles. When backing up a DataFile, RMAN would ignore
> __unused__ blocks --- blocks that have never been used.
> Now, the part where I don't agree with Mladen is about reading the
> bitmap information from the tablespace header. RMAN can backup
> DataFiles belonging to Dictionary Managed Tablespaces without
> Automatic Segment Space Management. In such cases there is no
> bitmap in the tablespace header to read from.
>
> When Oracle creates a DataFile it initializes the file with NULLs.
> When
> a block is used [written to as a Table Row-Block or an Index
> Leaf-Block],
> the block has to be formatted before it is written-to. Once it is
> formatted
> [the formatting is the block header, table column names, and
> possibly
> the initrans area and pctfree area], the block will always remain
> "used"
> even if all the rows in it are deleted.
>
> Thus, when RMAN goes through a DataFile it examines each block and
> ignores unused blocks which have not been formatted.
>
> Such unused or empty blocks may be within an Extent or unallocated
> to any
> extent !
>
> Hemant
>
> At 08:13 AM 04-04-03 -0800, you wrote:
> >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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> Hemant K Chitale
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> Author: Hemant K Chitale
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> Author: Freeman Robert - IL
> INET: FREEMANR_at_tusc.com
>
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Hemant K Chitale
http://hkchital.tripod.com

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Author: Hemant K Chitale
  INET: hkchital_at_singnet.com.sg

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