UNDO

How to Resolve ORA-30012: undo tablespace does not exist or of wrong type

by Ed Chen
November 11, 2022November 13, 2022

ORA-30012 Tried to restart a normal database after changing the default undo tablespace, but it failed with ORA-30012. SQL> startup ORACLE instance started. ... Database… Read More »

PDB Local Undo for Each RAC Instance

by Ed Chen
June 16, 2021November 9, 2021

Usually, we have separate undo tablespace for each instance in a RAC database. For example, UNDOTBS1 is for the first instance and UNDOTBS2 is for… Read More »

How to Resolve ORA-01555 UNDO_RETENTION

by Ed Chen
April 8, 2016March 28, 2021

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 »

Oracle Undo Tablespace Usage

by Ed Chen
May 28, 2014February 2, 2022
2 Comments

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, 2012March 28, 2021

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 »