Undo Retention
The target period for preserving committed undo so long-running consistent reads and flashback operations can reconstruct older versions.
Oracle Runtime Context
Undo retention is the target period for preserving committed undo so long-running consistent reads and flashback operations can reconstruct earlier versions. If required undo is overwritten before an old snapshot finishes, the query can encounter a snapshot-too-old failure.
Guarantee Boundary
A configured target is not necessarily an absolute guarantee under every storage and workload condition. Undo tablespace capacity, generation rate, retention-guarantee configuration, and pressure from concurrent work determine what can actually be retained.