Re: Recover question: ALTER DATABASE USING BACKUP CONTROLFILE

<mokat67_at_hotmail.com> wrote in message
news:3e99db18.3088651_at_news.hccnet.nl...
> Supposing that I lost my online redo-log files and still in posession
> of controle and archive files
>
> I would like to know what is against the method:
>
> A) ALTER DATABASE USING BACKUP CONTROLFILE
I presume that should have read 'recover database using backup controlfile'.

> Instead of:
>
> B) Recover Database
>
> I know that method (A) is used when the latest control files are not
> available anymore.

No, it's used when the controlfile you've got is behind the timestamps on the datafiles, or when the database structure described by a perfectly up-to-date controlfile is not the database structure you actually want.

The controlfile is, amongst other things, the 'master clock' for the database. It's read first at startup and hence is deemed to set the SCN to which all the datafiles of the database should agree (barring read only tablespaces, of course). When the master clock is itself wrong, you need to tell Oracle to ignore it for SCN determination purposes.

The 'wrong structure' problem: suppose some looney junior DBA does a 'drop tablespace DATA'. The control file you've got now no longer has a pointer to the relevant datafiles, and knows nothing about this vitally important tablespace. You therefore restore the last good controlfile, which has such pointers within it, because the backup was taken before the tablespace was dropped. But now you have an old version of the control file (so, see above...)

>But if the current control files still exits is
> there a reason why not to choose for method (A) in combination with a
> cold backup restore action? What can be negative consequences if there
> are any?

Not sure I understand the question. If the control file you've got describes the database you want, and is bang up to date and in synchronism with the datafiles you have (or is in advance of where your restored datafiles have gotten to), then there is no need to issue your command A.

Regards
HJR
>
> Thanks
>
>
>
>
>
>
Received on Mon Apr 14 2003 - 04:57:04 CDT