If
the SYSTEM tablespace is locally managed, a default temporary tablespace must be defined when the
database is created.
When there is not enough space available in the user??™s default temporary tablespace, and
either the tablespace cannot be autoextended or the tablespace??™s AUTOEXTEND attribute is
disabled, the user??™s query or DML statement fails.
Too Much or Too Little Undo Space Allocated
As of Oracle9i, undo tablespaces have simplified the management of rollback information by
managing undo information automatically within the tablespace. The DBA no longer has to define
the number and size of the rollback segments for the kinds of activity occurring in the database.
As of Oracle 10g, manual rollback management has been deprecated.
166 Oracle Database 11g DBA Handbook
Not only does an undo segment allow a rollback of an uncommitted transaction, it provides
for read consistency of long-running queries that begin before inserts, updates, and deletes occur
on a table. The amount of undo space available for providing read consistency is under the control
of the DBA and is specified as the number of seconds that Oracle will attempt to guarantee that
???before??? image data is available for long-running queries.
As with temporary tablespaces, we want to make sure we have enough space allocated in an
undo tablespace for peak demands without allocating more than is needed. As with any tablespace,
we can use the AUTOEXTEND option when creating the tablespace to allow for unexpected growth
of the tablespace without reserving too much disk space up front.
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