Wednesday, November 7, 2007

Oracle 10g : Flash Back Drop

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· Flashback Drop :

This Feature provides a way to restore accidentally dropped tables.
Flashback Drop provides a safety net when dropping objects in Oracle Database 10g. When a user drops a table, Oracle places it in a recycle bin. Objects in the recycle bin remain there until the user decides to permanently remove them or until space limitations begin to occur on the tablespace containing the table. The recycle bin is a virtual container where all dropped objects reside. Users view the recycle bin and undrop the dropped table and its dependent objects.
Flashback Drop is available even after restarting the database.

Limitations and Restrictions on Flashback Drop :

· The recycle bin functionality is only available for non-system, locally managed tablespaces. If a table is in a non-system, locally managed tablespace, but one or more of its dependent segments (objects) is in a dictionary-managed tablespace, then these objects are protected by the recycle bin.

· There is no fixed amount of space allocated to the recycle bin, and no guarantee as to how long dropped objects remain in the recycle bin. Depending upon system activity, a dropped object may remain in the recycle bin for seconds, or for months.

· While Oracle permits queries against objects stored in the recycle bin, you cannot use DML or DDL statements on objects in the recycle bin.

· You can perform Flashback Query on tables in the recycle bin, but only by using the recycle bin name. You cannot use the original name of the table.

· A table and all of its dependent objects (indexes, LOB segments, nested tables, triggers, constraints and so on) go into the recycle bin together, when you drop the table. Likewise, when you perform Flashback Drop, the objects are generally all retrieved together , It is possible, however, that some dependent objects such as indexes may have been reclaimed due to space pressure. In such cases, the reclaimed dependent objects are not retrieved from the recycle bin.

· Due to security concerns, tables which have Fine-Grained Auditing (FGA) and Virtual Private Database (VPD) policies defined over them are not protected by the recycle bin.

· Partitioned index-organized tables are not protected by the recycle bin.

· The recycle bin does not preserve referential constraints on a table (though other constraints will be preserved if possible). If a table had referential constraints before it was dropped (that is, placed in the recycle bin), then re-create any referential constraints after you retrieve the table from the recycle bin with Flashback Drop.

For Flash Back Database >> Click Here

For Flash Back Table and Query >> Click Here

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