Re: Mimic incomplete recovery - Noarchivelog Mode

I would like to comment on this.
For closed/cold DB backups (after clean shutdown - not shutdown abort) it is not necessary to backup the redolog files. (This used to be documented in the Oracle Backup & Recovery docs)

When restoring from such a backup the DB is opened using 'open resetlogs'. The redolog
files are not necessary because no instance recovery is needed. When the DB is open with resetlogs the missing logfiles are created - the only thing is, the DB
is reset to a new incarnation.

So - a database in noarchivelog mode which is backed up every night by performing a clean
shutdown and putting every datafile & control file on tape can be restored and opened
with a resetlogs without mimic'ing an incompleted recovery and without dataloss.

"Richard Foote" <richard.foote_at_bigpond.com> wrote in message news:4cTr9.56196$g9.159869_at_newsfeeds.bigpond.com...
> Hi Nick,
>
> I agree this can all appear somewhat odd but we've got to make it a tad
> difficult else everyone will want a go :)
>
> When you open the database with RESETLOGS, you effectively blow away any
> online redo logs and reset the database to a new incarnation. Typically
you
> would only do such a thing when attempting an incomplete recovery as by
> definition you would have lost data (else why blow away the current redo
> log). Therefore there is a "flag" set in the control file that only
permits
> such an operation when all datafiles are in sync *after the successful
> completion of an incomplete recovery* after which time the flag is reset.
No
> incomplete recovery, no resetlogs.
>
> However, the other scenario when you may want to perform such an operation
> is when performing a restore recovery with a NOARCHIVELOG database without
> the restore of the redo logs. You want to blow away the redo logs from the
> point of time of backup because you have no such backups of the redo logs.
> Problem is this damn flag in the control file. It will insist you only
> perform resetlogs after the successful completion of an incomplete
recover.
> Hence the "dummy recovery" which effectively just sets this flag.
>
> It's not an issue per se but it is an extra step that needs to be
performed
> and it does require sysdba (rather than sysoper) privileges hence why many
> sites with noarchivelog databases include the redo logs in the backups
which
> can then be subsequently restored with the rest of the database and simply
> opened.
>
> Cheers
>
> Richard
> "Nick" <nick_hobbs_at_hotmail.com> wrote in message
> news:8ca3c5c7.0210180348.6a9358ac_at_posting.google.com...
> > Hi Folks,
> >
> > 8.1.7 on HP-UX 11i
> >
> > According to Oracle 8i Backup & Recovery pdf:
> >
> > When a NOARCHIVELOG database is restored to a new location (due to
> > media failure at the original location), DBA should mimic incomplete
> > recovery and cancel before opening the database with RESETLOGS
> > options.
> >
> > Question : What does the mimic of incomplete recovery actually
> > achieve? I'm told it is necessary to allow RESETLOGS when opening the
> > database. Does this mean the mimic is mandatory. Since the database
> > has had a full database restore and file names have been altered I'm
> > unclear as to why a faxed incomplete recovery should be necessary.
> >
> > BTW I would test it out but I'm on DB2 at present about to move to an
> > Oracle site.
> >
> > Any help appreciated.
> >
> > Regards
> >
> > Nick
>
>
Received on Fri Oct 18 2002 - 14:24:06 CDT