Question:
What is Oracle’s automatic undo management (AUM) and how to I use it
on my database?
Answer:
Oracle automatic undo management was introduced to relieve the DBA
tedium of sizing undo to remove the ORA-01555 snapshot too old error.
With AUM, Oracle manages the size of the rollback segments (later
re-named undo logs) to ensure that DML-intensive transactions can
complete successfully.
See my notes here on
using Oracle AUM.
Automatic unto
management is set by default in 11g (via the
undo_management=auto
parameter), but you can migrate to automatic undo in earlier releases
that support AUM by creating
an undo tablespace and set
undo_management=auto and bounce your database:
create undo tablespace
ts_undo
datafile
'/u01/oradata/prod/ts_undo.dbf'
size 2m reuse autoextend on;
alter system set undo_tablespace=ts_undo;
alter system set undo_management=auto;
