Re: question about rollback and redo

Ryan Gaffuri wrote:

> Documentation isnt too clear on this(or Im just not following it).
>
> When you do a delete the entire row is copied to the rollback segment.
> Now if Im deleting 1MB worth of data in the datafile(lets assume there
> is no pctfree or pct used, just data), will 1MB of data be written to
> rollback? Im assuming there will be less due to block header, etc...,
> but how much less?
>
> Now when the rollback is written to redo, how much data does that
> entail? What goes in a 'change vector'? Does the entire row get copied
> twice? Once to the rollback and once to the redo logs?

Keep in mind the purpose behind both "redo" & "rollback".

When a row is deleted, then to roll back the delete an INSERT with every populated field must be contained in the rollback segment.

When a row is deleted, to do again this action all that is needed in the redo logfile is a ROWID and a flag for delete.

When INSERTing data the REDO get more data written to it and the rollback just get the ROWID and an delete flag. Received on Fri Sep 19 2003 - 19:55:55 CDT