Re: Instance Recovery Question

Actually, until the commit is issued, the data is not written to the 'permanent' table block but is in the rollback segment block. Answer 1 is correct.

On commit, the rollback block is freed only after the table block is written. Should an instance fail between commit and rollback marked free, the block will be rewritten to the table.

We now enter the mystical and mythical territory of system buffer flushes, that is data corruption because Oracle wrote to the disk, but the system did not flush its buffers to disk. You cannot eliminate this risk (even with direct raw files), just get it to a minimum. There is no recovery, hence the magic of backups and archives.

In article <eZMrZPpH#GA.80_at_nih2naac.prod2.compuserve.com>,   "Jean-Philippe Squelbut" <squelbut_at_csi.com> wrote:
> Perhaps, you have not commited when your instance crashes.
> Won't it be ok that way ?
>
> AJG a écrit dans le message <36661AD3.891C007F_at_noemail.noemail>...
> >Hi,
> >
>
> >A change is made to a data block
> >That change is recorded in a rollback block
>
> >Change also recorded in log buffer
>
> >DBWR writes data block to disk
> >Instance crashes
> >- Change in log buffer not written to disk yet
> >- Rollback information not written to disk yet
> >This is a problem
> >
> >Two Solutions:
> >1) Oracle always writes out the rollback block before the changed data
> >block.
> >2) Oracle always waits to flush a change in log buffer to disk before
> >writting the changed block (data or rollback)
> >
> >2 sounds unlikely to me, so I'm going with 1.
> >
> >I'm I correct?
> >
> >Thanks!
> >
> >Alan.
> >
> >
> >--
> >Alan Gano
> >http://home.att.net/~alangano/index.html
> >
> >
> >
>
>

-----------== Posted via Deja News, The Discussion Network ==---------- http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own Received on Sat Dec 05 1998 - 14:09:00 CST