Undo and Redo

Quick and Rough Notes : Undo and RedoUndo is where Oracle logs how to reverse a transaction (one or more DMLs in a transaction)Redo is where Oracle logs how to replay a transactionUndo and Redo are written to as the transaction proceeds, not merely at the end of the transaction(imagine a transaction that consists of 1million single-row inserts, each distinct insert is written to undo and redo) Undo segmentsOracle dynamically creates and drops Undo segments depending on transaction volumeAn undo segment consists of multiple extents.