Re: backup without archivelog mode

"Howard J. Rogers" wrote:
>
> "Sean M" <smckeownNO_at_BACKSIESearthlink.net> wrote in message
>
> > Now who's nitpicking (are not unrecoverable transactions, by definition,
> > unrecoverable?)? But fine, I'll play along. If "by some other means"
> > you're referring to repeating the original operation (direct SQL*Loader
> > jobs, direct load inserts, etc.), then I agree, you can "recover" it.
> > But that's true of *any* transaction, logging or not. Any transaction
> > is "recoverable" under your definition by simply doing it over again.
> > The trick is knowing/remebering what you did.
> >
>
> But the point is that for a regular piece of DML, you would indeed have to
> remember it to reperform it. The updated data doesn't exist anywhere else
> other than in the table.

No. Just because a peice of DML was logged doesn't mean you don't have a record of it elsewhere. To play off your example, just think of a *non*-direct SQL*Loader job. Or master -> slave replication.

> Hence redo is needed to reperform it. But Direct
> SQL Loads don't need to be remembered at all. The text file which was the
> source of the load still exists (we presume: at least, it's bad practice to
> delete it until a new backup of the relevant tablespace has been performed).
> All you'd need to do is re-perform the load.

Ah, but therein lies the crux yes? As I said, that's the trick. But it has nothing to do with logging vs. nologging. In either type of DML, nothing is stopping you from 1) keeping enough information around through "some other means" to recreate the lost information or 2) throwing caution to the wind and destroying the source immediately after the operation.

> So no, not all transactions are "recoverable" under my definition. Regular
> DML is only recoverable through redo, since the source of the transaction is
> only in your head. Transactions which respect the nologging keyword don't
> need redo, because the source data is available in tangible form elsewhere.

Plenty of assumptions there. Again, regular DML needn't only be in someone's head, and the source nologging DML can certainly be lost before the next backup of the affected datafiles.

As to the rest of your post, let's take it offline.

Regards,
Sean Received on Sat Mar 23 2002 - 19:02:20 CST