Rollback Segment vs Redo log

Hi guys, I have come across below paragraph today …

“ A Rollback Segment is a database object containing before-images of data written to the database. Rollback segments are used to:
• Undo changes when a transaction is rolled back
• Ensure other transactions do not see uncommitted changes made to the database
• Recover the database to a consistent state in case of failures “
My understanding is that Oracle also stores before image for committed and uncommitted transactions in the redo-log files! So the question is why does Oracle need rollback segment? Why cant Oracle provide rollback functionality/read consistency and recovery by using the redo log files?
Thanks!

For back up recovery Oracle uses Redo logs.

Before data committed you need Undo segments data.
After commit you need Redo log data to recover.

Quote:

---

Originally Posted by khoshtip_uk

Hi guys, I have come across below paragraph today …

“ A Rollback Segment is a database object containing before-images of data written to the database. Rollback segments are used to:
• Undo changes when a transaction is rolled back
• Ensure other transactions do not see uncommitted changes made to the database
• Recover the database to a consistent state in case of failures “
My understanding is that Oracle also stores before image for committed and uncommitted transactions in the redo-log files! So the question is why does Oracle need rollback segment? Why cant Oracle provide rollback functionality/read consistency and recovery by using the redo log files?
Thanks!

---

that is one of the most basic concepts of oracle - in fact the most important one

go and read the concepts manual

your statement about redo logs is very very wrong