An example - Snapshot too old

Snapshot too old

User SCOTT has updated the EMP table and has not committed the changes. The old values of the rows updated by SCOTT are written to the undo segment. When user JAKE queries the EMP table, Oracle uses the undo segment to produce a read-consistent view of the table. If JAKE initiated a long query, Oracle fetches the blocks in multiple iterations. User SCOTT can commit his transaction, and the undo segment is marked committed. If another transaction overwrites the same undo segment, JAKE’s transaction will not be able to get the view of the EMP table when the transaction started. This produces a snapshot too old error.