Re: REDO LOG Concepts
- From: "Daniel W. Fink" <daniel.fink@xxxxxxxxxxxxxx>
- To: DBA Deepak <oracle.tutorials@xxxxxxxxx>
- Date: Wed, 16 May 2007 21:52:07 -0600
Deepak,
I'll have to leave the detailed explanations of file systems, files and
i-nodes to the unix gurus, and any mistakes are likely due to my inexact
understanding of these concepts.
The rm command is not placed in a queue, but works to remove file system
information about the file you are removing. However, any process that
still has the file open (or locked if you prefer this way of thinking of
it) still has that file system information. It can still read from and
write to that file, but any process that attempts to open the file will
not find the file system information and so that attempt fails. Once all
of the processes that have the file open, all file system information
about that file is gone.
In your scenario, the update is committed, so it cannot be rolledback. A
SHUTDOWN NORMAL, IMMEDIATE or TRANSACTIONAL will have no uncommitted
transactions within the database (everything is either committed or
rolled back...no in between).
Let's say you issued a SHUTDOWN ABORT after the update, then the
database might contain uncommitted transactional data. Upon instance
startup, it will attempt to rollback any uncommitted transactions by
reading the redo log...but you've deleted the redo logs, therefore all
the information to rollback the transaction is gone.
--
Daniel Fink
Oracle Performance, Diagnosis and Training
OptimalDBA http://www.optimaldba.com
Oracle Blog http://optimaldba.blogspot.com
Join me at Miracle Scotland DB Forum!
http://www.miracleltd.com/index.asp?page=167&page2=343
DBA Deepak wrote:
Hi Daniel,
I did not try for other processes. But will the rm command in OS
command queue? Is there any posibility to rollback the delete when the
instance is open? And if at all it is possible will the commited
transactions be reclaimed?
Deepak
--
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