Re: RMAN impact

From: Mark Brinsmead <pythianbrinsmead_at_gmail.com>
Date: Tue, 24 Oct 2006 22:08:07 -0600
Message-ID: <cf3341710610242108h57f8bd6ci57f0e9b9291cd476@mail.gmail.com>

Chris,

Perhaps I have misread the documentation. Here is the relevant section of the 10g "Backup and revoery Reference":

CHECK LOGICAL

Tests data and index blocks that pass physical corruption checks for logical corruption, for example, corruption of a row piece or index entry. If RMAN finds logical corruption, then it logs the block in the alert.log and server session trace file.
If the sum of physical and logical corruptions detected for a file is no more
than its MAXCORRUPT setting, then the backup command completes, and V$DATABASE_BLOCK_CORRUPTION is populated with any corrupt block ranges. If there are more thanMAXCORRUPT corrupt blocks, then the command terminates without updating the view and no output file is created for the backup.
If the initialization parameter DB_BLOCK_CHECKSUM=TRUE, and if MAXCORRUPT and NOCHECKSUM are not set, then specifying CHECK LOGICAL detects all types of corruption that are possible to detect. Note: The MAXCORRUPT setting specifies the total number of physical and logical corruptions permitted on a file.

Those are pretty strong words, even coming from an Oracle manual. ;-)

It is my understanding that an RMAN "BACKUP VALIDATE" with "CHECK LOGICAL" can, indeed, detect the sorts of corruption you are referring to. I've even used it for
such purposes on a couple occasions -- but since the results were "negative" I can't
say for certain that it really works... ;-)

On 10/24/06, Christian Antognini <Christian.Antognini_at_trivadis.com> wrote:
>
> Hi Mark
>
> Just a couple of comments...
>
> ...
>
> Be carefull... CHECK LOGICAL doesn't cover all type of logical
> corruptions. Inconsistencies, e.g. ORA-01499, are *not* detected. AFAIK
> ANALYZE is the only tool able to discover them.
>
>
> Regards,
> Chris
>

-- 
Cheers,
-- Mark Brinsmead
   Senior DBA,
   The Pythian Group
   http://www.pythian.com/blogs

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Received on Tue Oct 24 2006 - 23:08:07 CDT