August 2011
Intermediate to advanced
576 pages
16h 12m
English
Oracle stores the original values of the data called before an image in undo segments. The data stored in an undo segment is used to provide read consistency and to roll back uncommitted transactions. Starting with Oracle 10g, the flashback feature also makes use of undo data.
Oracle provides two methods of undo management: automatic undo management and manual undo management.
Automatic undo management was introduced in Oracle Database 9i R1 and is highly recommended. In this method an Oracle instance uses a tablespace of type “undo” to store undo/ rollback data. The instance creates the required number of undo segments in the dedicated tablespace and allocates them to transactions to store the undo ...
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