Re: ALTER DATABASE NORESETLOGS?

"Steve Jones" <steve.jones_at_takethisoutproact.net> wrote in message news:39a3f80f_1_at_nnrp1.news.uk.psi.net...
> What exactly does ALTER DATABASE NORESETLOGS do during recovery?
>

Do it the other way around. If you ever issue the command 'alter database open resetlogs', it will be done after an incomplete recovery (ie, you did a 'recover until cancel', or a 'recover until time x' etc). The trouble with an incomplete recovery is that although you have rolled the data files forward in time, from the time of the last backup to the specified point of halting the recovery process, your Control Files and Redo Logs are left sitting at the time of the failure that prompted the recovery process in the first place. In other words, they are at a time *ahead* of the datafiles.

Yet you don't want to apply any more Redo to the datafiles.

So how to force the Control Files and Redo Logs to synchronise 'backwards' with the datafiles? That's what the 'resetlogs' option does -it's a bit of a sledgehammer approach, but issuing that command forces your entire database back to checkpoint (ie, 'timestamp') 1: Control Files are now at time 1, as are all datafiles and Redo Logs -the database is thus synchronised, and can be opened for business.

Knowing that, you can now see what 'noresetlogs' does -or rather, what it doesn't do! It's a bit of an unusual option to specify, because it's the default option for the 'alter database open' command, and -being the default- doesn't actually need to be specified. The database is opened with all the files left at their usual checkpoint sequence number. That can only happen, of course, if all those checkpoint numbers agree with each other -and that will only be the case after a *complete* recovery, not an incomplete one. (It's also the situation that applies when nothing nasty has happened to your database at all, of course!)

HTH
Regards
HJR
> --
> Steve Jones
> ProAct International, 9a Vale Street, Denbigh, North Wales
> stevej_at_getridofthisproact.net
>
>
Received on Fri Aug 25 2000 - 16:50:32 CDT