Re: how does oracle apply rollback?

Ryan Gaffuri wrote:
>
> 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.

I don't think its done with anything reminiscent of SQL. If you dump out undo blocks, they typically contain just the bare bones of what is required to undo a change. eg for an insert, just the rowid; for a delete, all the "row" etc.

online rebuild is somewhat different. It appears to be equivalent to a materialised view, namely, you start rebuilding and store a journal table of changes that get applied once the rebuild is complete.

hth
connor

-- 
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Connor McDonald
http://www.oracledba.co.uk

"Some days you're the pigeon, some days you're the statue"