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Home -> Community -> Usenet -> c.d.o.server -> Re: recovery with until cancel and without
"yls177" <yls177_at_hotmail.com> wrote in message
news:c06e4d68.0405202128.1da062e1_at_posting.google.com...
> from my understanding after reading the posts, i realized that with
> until cancel, oracle will recover till the databae crash or have some
> problems.
No, "recover until cancel" means "keep applying redo until I tell you to stop". You pick the point where you want to type the word "cancel", and hence it has nothing to do with the point where the database crashes, necessarily.
>after this, u can alter database open resetlogs for oracle
> to start fine but then u will lose some data, right?
If you ever stop applying redo before the point where Oracle would naturally stop applying it, then by definition you have not applied some redo that was generated by transactions. Therefore, you have not repeated those transactions. Therefore, you have lost data.
It' called an "incomplete recovery" for a reason.
> and if u dont use until cancel, oracel will automatically recover by
> itself.
Well, sort of. You have to type in the words "recover database", so it's hardly automatic. But yes, if you don't use the words 'until cancel' or 'until time' then Oracle will apply every last drop of redo.
> but then i still dont think that it makes a difference, only that with
> until cancel, oracle will stop recovering till the time which it
> crashed.
It's got nothing to do with when the database crashed. Instance crashes don't even need any manual recovery commands at all. Instance recoveries really are totally and utterly automatic.
> also, i have searched google and from below
I'd suggest http://tahiti.oracle.com. There's a lot about recovery you don't seem to be getting. Which is fair enough, but you need to nail this subject.
>
>
> quote:
> --------------------------------------------------------------------------
Precisely so. Spot on. Ordinarily, the control file is our 'master clock' and tells us the SCN to which all the datafiles should be synchronised. The 'using backup controlfile' clause tells Oracle not to pay any attention to what the control file says, because you've flagged it to be well out of date before you start.
>I could further theorise that "UNTIL CANCEL" overrides
> this
> behaviour and lets you terminate the restore at any point without
> regard to
> the SCNs stored in the datafile headers.
They're not mutually exclusive. Until cancel means, as I've said, "apply redo (ie, recover) until I tell you to stop". The "using backup controlfile" means "and don't trust what the control file tells you". You can do the one without the other. It depends on whether you can trust what the control file's SCN is (if you haven't restored it from a backup, then yes you can).
> Mind you without going and playing with a recovery this is all
> conjecture.
> If anyone can authoritatively confirm or deny this I'd appreciate it
> as it
> doesn't seem to be documented anywhere.
Well, that's a bit silly. Of course it's documented. In lots of places. That the documentation provided by Oracle might not be terribly understandable is a rather different matter.
You first need to get the distinction between complete and incomplete recoveries clear in your head.
Then you need to understand that all recoveries, complete and incomplete work by knowing what the control file's SCN is.
Then you will understand what a mess you'll be in when the control file's SCN is known to be wrong, and why you need a mechanism to tell Oracle 'don't trust it'.
And then you'll see that you can do a complete recovery 'using backup controlfile' just as well as you can do an incomplete recovery 'using backup controlfile'.
Regards
HJR
Received on Fri May 21 2004 - 05:56:49 CDT
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