RE: split block (torn page) problem

From: <rajendra.pande_at_ubs.com>
Date: Thu, 8 Dec 2011 09:47:25 -0500
Message-ID: <D4C8B99EB96F2C42B4E19A3B87664F5E02AC9787_at_NSTMC612PEX.ubsamericas.net>

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_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Riyaj Shamsudeen Sent: Thursday, December 08, 2011 12:23 AM To: Laimutis.Nedzinskas_at_seb.lt
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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Received on Thu Dec 08 2011 - 08:47:25 CST