Re: can somebody help what exactly the rollback segment and redo log files contain..

The redo log contains both the new values as well as the undo information. Undo is just another block type in the database that gets logged. If you did'nt commit you txn and the instance crashed but the blocks had made it to disk - after doing rollforward recovery you'd now have the new value in the block which was'nt commited so you'd need the undo to roll it back.

"andrija" <ar35644_at_fer.hr> wrote in message news:<9qomt9$b553$1_at_as201.hinet.hr>...
> "sudhakar Marampelly" <marampelly_s_at_bharatmail.com> wrote in message
> news:50e5f826.0110182056.2db4a3ec_at_posting.google.com...
> > Hai!
> >
> > iam having some doubt in oracle..
> > let me explain a scenario..
> > there is a table A in the database with 1,2,3 rows..
> > now you are inserting a new row 4 into table A.
> > so what are the additions to the rollback segment and redo-log file as
> > well..
> > please some body help me..what exactly the rollback segment and
> > redolog files contain..how it will be helpful incase of a recovery..
> >
> > what i understood in was that..
> > if a value x=4 is there in the D/B and you are changing the value to a
> > new value..let say x=7..then rollback segment will have the old
> > value(x=4) and redo log file will have both x=4 and x=7..
> > please somebody help me to get of this problems..
> >
> > thanks in advance..
> > regards
> > Sudhakar Marampelly
>
> I don't thik that redo log will have both values (vhat's the point of redo
> log then?).
> Thing is, when you finish your transaction which inserts or changes data in
> the table, changes will not be written on disk immediately. Changes are in
> memory until DBW process writes them down. If there is a, let's say, power
> failure before DBW writes changes down, on startup Oracle will search the
> redo-log and roll-forward your transaction.
Received on Sun Oct 21 2001 - 04:50:47 CEST