You don??™t need to change your undo tablespace size immediately; the beauty of Undo
Advisor is that you can change the time period for analysis and retention to see what your disk
requirements will be in a given scenario.
FIGURE 6-14 Undo Advisor recommendations
CHAPTER
7
Managing Transactions
with Undo Tablespaces
207
208 Oracle Database 11g DBA Handbook
n Chapter 6, we touched briefly on how the space in an undo tablespace is
managed, along with views such as V$UNDOSTAT that can help the DBA monitor
and size the undo tablespace. In this chapter, we??™ll delve much more deeply into
the configuration and management of the undo tablespace, and how we may
resolve the sometimes conflicting requirements of providing enough undo for read
consistency while preventing the failure of DML statements because the undo retention parameter
is set too high.
To start off this chapter, we??™ll do a quick review of transactions from a database user??™s point of
view so that you will better understand how to support the user??™s transactions with the appropriately
sized undo tablespace. Next, we??™ll cover the basics of how to create an undo tablespace, either
during database creation or later using the familiar create tablespace command. Undo segments
fulfill a number of requirements for database users, and we will enumerate and explain each of
those requirements in some detail.
Oracle provides a number of ways to monitor and, as a result, more precisely size undo
tablespaces.
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