Re: Lost Online Redo, checkpoints
- From: Hemant K Chitale <hkchital@xxxxxxxxxxxxxx>
- To: Laimutis.Nedzinskas@xxxxxxxxxxxxx, <oracle-l@xxxxxxxxxxxxx>
- Date: Sun, 13 May 2007 01:04:26 +0800
No, there is no contradiction.
If the LGWR is unable to write to the Active Redo
Log file, it crashes and the Database Instance also crashes.
At the next restart, Oracle attempts an Instance Recovery.
If the Active Redo Log file is NOT available,
then you have no choice but to restore a backup and roll-forward
to the last available ArchiveLog +, if possible,
RedoLog that was Current but not yet Archived.
If the Active Redo Log file is available, the
Instance Recovery goes through and the Database is OPENed.
The LGWR may fail writing because of any of different reasons :
a. The file has really been deleted
b. The filesystem went offline for a while but
was made available again by the System/Storage Adminsitrator
at the next startup.
Hemant
At 10:34 PM Thursday, Laimutis Nedzinskas wrote:
<snip>
If the *current* redo log is lost then
- Will Oracle halt? I think yes.
What happens if checkpoint crashes in the middle
and the corresponding redo logs(those containing
changes for checkpoint) are lost. As far as I
understand the database could not be recovered without restore from backup.
<snip>
Except that at some point in this doc Oracle states that:
...
If the group is Current - Attempt to clear the
log; if impossible, then you must restore a
backup and perform incomplete recovery up to the
most recent available redo log.
...
But bellow Oracle states that:
... The current log is the one LGWR is currently
writing to. If a LGWR I/O fails, then LGWR
terminates and the instance crashes ...
(which is supported by my practical experience)
Isn´t this a contradiction?
Hemant K Chitale
http://web.singnet.com.sg/~hkchital
and
http://hemantscribbles.blogspot.com
and
http://hemantoracledba.blogspot.com
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