UNDO

How to Resolve ORA-01555 UNDO_RETENTION

by Ed Chen
April 8, 2016October 31, 2019

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, 2016November 1, 2019

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 »

How to Resolve ORA-01562: failed to extend rollback segment number

by Ed Chen
May 13, 2015March 30, 2018

Found repeated errors in the alert log:...ORA-01562: failed to extend rollback segment number 96...It seemed that some transactions were doing DML, but they failed to… Read More »

How to Check UNDO Tablespace Usage

by Ed Chen
May 28, 2014October 31, 2019

The first purpose of using UNDO is for storing all uncommitted data in case we need to undo uncommitted data in rollback or after system… Read More »

How to Resolve ORA-30036 UNABLE TO EXTEND SEGMENT BY 8 IN UNDO TABLESPACE 'UNDOTBS1'

by Ed Chen
October 19, 2012October 31, 2019

ORA-30036 This error ORA-30036 could be very serious in a situation that is described below and may make users panic: One day, a DBA was… Read More »