RE: split block (torn page) problem
- From: <rajendra.pande@xxxxxxx>
- To: <riyaj.shamsudeen@xxxxxxxxx>, <Laimutis.Nedzinskas@xxxxxx>
- Date: Thu, 8 Dec 2011 10:00:22 -0500
http://www.oracle.com/us/technologies/linux/linux-emulex-prevent-corrupt
ion-wp-193087.pdf
Cant find the ORACLE presentation
Thanks
Raj Pande
http://goto/employeeid/43190252
-----Original Message-----
From: Pande, Rajendra
Sent: Thursday, December 08, 2011 9:47 AM
To: riyaj.shamsudeen@xxxxxxxxx; Laimutis.Nedzinskas@xxxxxx
Cc: ORACLE-L
Subject: RE: split block (torn page) problem
There was an interesting presentation from ORACLE on similar issue
The topic was "silent Data loss" (or something along these lines)
As a solution I believe ORACLE has come up with a logic that I believe
has now been released to hardware vendors - implemented together with
hardware vendors - at this time only emulex was mentioned
In that solution the oracle kernel creates a checksum and waits for the
confirmation of the checksum from the hardware level and till that is
received the IO is not marked as complete
Thanks
Raj Pande
http://goto/employeeid/43190252
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Riyaj Shamsudeen
Sent: Thursday, December 08, 2011 12:23 AM
To: Laimutis.Nedzinskas@xxxxxx
Cc: ORACLE-L
Subject: Re: split block (torn page) problem
Hi
crash recovery applies redo records to roll forward the changes. If a
modified block is not written yet to the disk, that is okay, as redo
records from the log files can be used to replay the changes.
But, if the block is not written properly or fractured, then the crash
recovery will raise corruption errors and can't correct the corruption.
In enterprise servers, server reboots does not cause any corruption
(usually). From oracle point of view, a buffer is filled with block
image
and I/O submitted to the OS. If the OS splits the call in to smaller
chunks
(say 4K) and writes with two atomic calls underneath the write system
call
(and that first 4K chunk succeeded, second 4K chunk write did not
succeed),
it is possible for the corruption to occur, but it is a corner case and
you
must be very unfortunate :-)
With ASM, file system caching is not involved and write calls operate
on
devices. So, probability is much less with ASM.
HTH
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>
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