Re: split block (torn page) problem

  • From: Riyaj Shamsudeen <riyaj.shamsudeen@xxxxxxxxx>
  • To: Laimutis.Nedzinskas@xxxxxx
  • Date: Tue, 6 Dec 2011 18:22:43 +0530

There will be corruption in this case as the head and tail piece of the
block might not match etc. So, there would be a need for block media
recovery or restore snf recovery to repair that corrupt block. Simply, this
is a corruption induced by hardware problem.
Cheers

Riyaj Shamsudeen
Principal DBA,
Ora!nternals -  http://www.orainternals.com - Specialists in Performance,
RAC and EBS
Blog: http://orainternals.wordpress.com
OakTable member http://www.oaktable.com and Oracle ACE Director

Co-author of the books: Expert Oracle
Practices<http://tinyurl.com/book-expert-oracle-practices/>,
Pro Oracle SQL,  Expert PL/SQL
Practices<http://tinyurl.com/book-expert-plsql-practices>



On Tue, Dec 6, 2011 at 2:38 PM, <Laimutis.Nedzinskas@xxxxxx> wrote:

> Hi
>
> Recently people blogged about very basic, core oracle functionality and
> issues with durability and isolation here:
> http://jonathanlewis.wordpress.com/2011/08/19/redo-2/
>
> Now I have a similar basic question about split block (torn page) problem.
>
> According to
>
> http://www.emc.com/collateral/hardware/solution-overview/h2603-oracle-db-emc-symmetrix-stor-sys-wp-ldv.pdf
>  EMC has a (separately licensed) feature Generic SafeWrite which "is used
> to help protect critical application from incurring an incomplete write,
> and subsequent torn page, due to a failure within a component"
>
>
> The question is what happens when:
>
> - Oracle dbwr(or foreground process for that matter) issues a single IO
> kernel call to write 8k block into a datafile
>
> - the first 4k are written successfully and the next 4k fails, i.e. torn
> page situation arises
>
> - Oracle is stopped, the problem is fixed, oracle is started and attempts
> crash recovery
>
> - My understanding is that Oracle crash recovery can not handle
> split-block. Unless the database was in backup mode meaning full block
> image is saved in the redo stream as a starting recovery point. I can only
> speculate the whole 8k image is so important because crash recovery needs
> datafile block sturctures like row directory (may be ITL's too ?) to be in
> a good shape.
>
> - Basically, is it so that Oracle relies on hardware atomicity with respect
> to 8k(or whatever block size) IO calls ? Is it so that the whole 8k block
> must be stored or nothing?
>
>
> Brgds, Laimis N
>
> --
> http://www.freelists.org/webpage/oracle-l
>
>
>


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