Re: how does oracle apply rollback?

Redo logs and rollback segments/undo both take part in guaranteeing data consistency. Summarizing, redo logs the operations involved while rollback/undo stores previous values until transaction commits. As a bonus, rollback is valuable to queries started before the delete/update transaction. When del/upd trans has committed, past queries may get ORA-1555 if rollback is recycled.

I don't know what you mean with "high level". For datafiles, each update starts immediately (it may be eventually rollbacked later). For users, changes are viewable only:
- after (and only if) the transaction is committed - only if their query is started after commit time

Umberto

"Ryan Gaffuri" <rgaffuri_at_cox.net> wrote in message news:1efdad5b.0307290412.1f8ff699_at_posting.google.com...
> Does Oracle do a high level 'update' statement between the rollback
> data and the table. I would think that this would not be possible
> since rollback is stored differently.
>
> what about redo? Or what about when you do an 'online' index
rebuild,
> someone else updates and when complete you need to apply the
changes.
>
> anyone know how the algorithms differ from a generic update
statement?
>
> I dont need to know. Im just curious.
Received on Sun Aug 03 2003 - 06:15:48 CDT