Using Flashback Drop and Managing the Recycle Bin - Oracle 10g

When you drop a table, the database does not immediately remove the space associated with the table. The database renames the table and places it and any associated objects in a recycle bin, where, in case the table was dropped in error, it can be recovered at a later time. This feature is called Flashback Drop, and the FLASHBACK TABLE statement is used to restore the table. Before discussing the use of the FLASHBACK TABLE statement for this purpose, it is important to understand how the recycle bin works, and how you manage its contents.

This section contains the following topics:

  • What Is the Recycle Bin?
  • Renaming Objects in the Recycle Bin
  • Viewing and Querying Objects in the Recycle Bin
  • Purging Objects in the Recycle Bin
  • Restoring Tables from the Recycle Bin

What Is the Recycle Bin?

The recycle bin is actually a data dictionary table containing information about dropped objects. Dropped tables and any associated objects such as indexes, constraints, nested tables, and the likes are not removed and still occupy space. They continue to count against user space quotas, until specifically purged from the recycle bin or the unlikely situation where they must be purged by the database because of tablespace space constraints.

Each user can be thought of as having his own recycle bin, since unless a user has the SYSDBA privilege, the only objects that the user has access to in the recycle bin are those that the user owns. A user can view his objects in the recycle bin using the following statement:

SELECT * FROM RECYCLEBIN;

When you drop a tablespace including its contents, the objects in the tablespace are not placed in the recycle bin and the database purges any entries in the recycle bin for objects located in the tablespace. The database also purges any recycle bin entries for objects in a tablespace when you drop the tablespace, not including contents, and the tablespace is otherwise empty. Likewise:

  • When you drop a user, any objects belonging to the user are not placed in the recycle bin and any objects in the recycle bin are purged.
  • When you drop a cluster, its member tables are not placed in the recycle bin and any former member tables in the recycle bin are purged.
  • When you drop a type, any dependent objects such as subtypes are not placed in the recycle bin and any former dependent objects in the recycle bin are purged.

Renaming Objects in the Recycle Bin

When a dropped table is moved to the recycle bin, the table and its associated objects are given system-generated names. This is necessary to avoid name conflicts that may arise if multiple tables have the same name. This could occur under the following circumstances:

  • A user drops a table, re-creates it with the same name, then drops it again.
  • Two users have tables with the same name, and both users drop their tables.

The renaming convention is as follows:
BIN$unique_id$version
where:

  • unique_id is a 26-character globally unique identifier for this object, which makes the recycle bin name unique across all databases
  • version is a version number assigned by the database

Viewing and Querying Objects in the Recycle Bin

Oracle Database provides two views for obtaining information about objects in the recycle bin:

Viewing and Querying Objects in the Recycle Bin

One use for these views is to identify the name that the database has assigned to a dropped object, as shown in the following example:


You can also view the contents of the recycle bin using the SQL*Plus command SHOW RECYCLEBIN.


You can query objects that are in the recycle bin, just as you can query other objects.

However, you must specify the name of the object as it is identified in the recycle bin. For example:

SELECT * FROM "BIN$yrMKlZaVMhfgNAgAIMenRA==$0";

Purging Objects in the Recycle Bin

If you decide that you are never going to restore an item from the recycle bin, you can use the PURGE statement to remove the items and their associated objects from the recycle bin and release their storage space. You need the same privileges as if you were dropping the item.

When you use the PURGE statement to purge a table, you can use the name that the table is known by in the recycle bin or the original name of the table. The recycle bin name can be obtained from either the DBA _ or USER _RECYCLEBIN view as shown in "Viewing and Querying Objects in the Recycle Bin" The following hypothetical example purges the table hr.int_admin_emp, which was renamed to BIN$jsleilx392mk2=293$0 when it was placed in the recycle bin:

PURGE TABLE BIN$jsleilx392mk2=293$0;

You can achieve the same result with the following statement:

PURGE TABLE int_admin_emp;

You can use the PURGE statement to purge all the objects in the recycle bin that are from a specified tablespace or only the tablespace objects belonging to a specified user, as shown in the following examples:


Users can purge the recycle bin or their own objects, and release space for objects, by using the following statement:

PURGE RECYCLEBIN;

If you have the SYSDBA privilege, then you can purge the entire recycle bin by specifying DBA_RECYCLEBIN, instead of RECYCLEBIN in the previous statement. You can also use the PURGE statement to purge an index from the recycle bin or to purge from the recycle bin all objects in a specified tablespace.

Restoring Tables from the Recycle Bin

Use the FLASHBACK TABLE ... TO BEFORE DROP statement to recover objects from the recycle bin. You can specify either the name of the table in the recycle bin or the original table name. An optional RENAME TO clause lets you rename the table as you recover it. The recycle bin name can be obtained from either the DBA_ or USER_ RECYCLEBIN view as shown in "Viewing and Querying Objects in the Recycle Bin". To use the FLASHBACK TABLE ... TO BEFORE DROP statement, you need the same privileges you need to drop the table. The following example restores int _admin _emp table and assigns to it a new name:


The system-generated recycle bin name is very useful if you have dropped a table multiple times. For example, suppose you have three versions of the int2 _admin _ emp table in the recycle bin and you want to recover the second version. You can do this by issuing two FLASHBACK TABLE statements, or you can query the recycle bin and then flashback to the appropriate system-generated name, as shown in the following example:



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