Rollback Segment vs Redo Log

Hi All,

OK, I'll admit I'm confused.

1. In Oracle, is there a difference between Rollback segment(s) vs Redo Log(s) ?
2. If the Rollback segment and Redo Log are 2 different entities, is a transaction's uncommitted modifications stored in the Redo Log ? (it should already be stored in the Rollback segment)
3. If the Rollback segment and Redo Log are 2 different entities, would it be conceptually correct to view them as follows:

   3.1 Redo Log:

       Persistent record of modifications from committed
         transactions.
       This allows delayed write of the dirty disk buffers
         associated with the commited transactions.

   3.2 Rollback Segment:
       Stores modifications of as yet uncommitted transactions.
       This allows application to rollback the current transaction.

4. One needs to size the Rollback Segments large enough to handle the largest amount of modification possible from any transaction.

But what about the Redo Log Buffer (LOG_BUFFER) ? Is the penalty for not having a large enough Redo Log Buffer simply that of poorer performance, or will it cause large transactions to end with exceptions ?

5. When the database is recovering, it performs roll-forward using the archive redo logs. Can it perform the subsequent roll-back using just the archive redo logs or does it need to use the rollback segments ?

Thanks for any clarification!

/Meh-Lit Received on Wed May 18 2005 - 19:50:12 CDT