TAILIEUCHUNG - OCA /OCP Oracle Database 11g A ll-in-One Exam Guide- P79

OCA /OCP Oracle Database 11g A ll-in-One Exam Guide- P79:There is an ever increasing demand for staff with IT industry certification. The benefits to employers are significant—they can be certain that staff have a certain level of competence—and the benefits to the individuals, in terms of demand for their services, are equally great. Many employers are now requiring technical staff to have certifications, and many IT purchasers will not buy from firms that do not have certified staff. | OCA OCP Oracle Database 11g All-in-One Exam Guide 736 The Flashback Data Archive The three flashback technologies discussed so far Flashback Database Flashback Drop and the various forms of Flashback Query can be useful but they all have limited flashback capability. A Flashback Data Archive can be configured to guarantee the ability to flash back a table to any time perhaps to a time years ago. It can also guarantee that data is removed when it has expired. Architecturally Flashback Data Archive requires one or more tablespaces various segments for each protected table and a new background process the FBDA process. The DBA must create the tablespace s and the archive s within them specifying a retention period for each archive and then nominate tables to be protected by an archive. The necessary segments will be created automatically and the FBDA will start when required. Users and application software will not be aware of any change so far as DML is concerned. Some DDL commands such as DROP and TRUNCATE will not be usable against protected tables as they would remove information from the data dictionary needed to interpret information in the archive. Flashback query commands such as a SELECT with the AS OF clause will execute successfully against versions of the table within the time frame specified for the archive protecting the table. To use the Total Recall facility implemented by Flashback Data Archives first create a tablespace. It is technically possible to create the archive s in a preexisting tablespace but it makes sense to separate them from regular data. Then create the archive specifying a tablespace a retention time and optionally a quota. For example create flashback archive default hrarch tablespace fbda1 quota 10g retention 5 year This command includes the DEFAULT keyword which means that it will be used as the archive for all tables unless specified otherwise. The default archive can also be set later alter flashback archive hrarch set default .

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