Automatic Undo Management

How to Resolve ORA-01555 UNDO_RETENTION

by Ed Chen
April 8, 2016December 11, 2022

ORA-01555 UNDO_RETENTION Let's see the error ORA-01555 UNDO_RETENTION first: Description ORA-01555: snapshot too old: rollback segment number string with name "string" too small Cause rollback… Read More »

UNDO_RETENTION, How and Why

by Ed Chen
April 7, 2016December 11, 2022

UNDO_RETENTION At times, you may find out or feel that UNDO_RETENTION is useless at all. Raising the number of seconds cannot resolve ORA-01555. This is… Read More »

How to Resolve SMON: about to recover undo segment xx SMON: mark undo segment xx as available

by Ed Chen
July 12, 2015March 30, 2018

Repeated messages were found in the alert log after instance startup:...SMON: about to recover undo segment 32SMON: mark undo segment 32 as availableSMON: about to recover… Read More »