|Oracle® Database Administrator's Guide
11g Release 1 (11.1)
|PDF · Mobi · ePub|
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
TABLE statement is used to restore the table. Before discussing the use of the
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:
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.
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:
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
You can enable and disable the recycle bin with the
recyclebin initialization parameter. When the recycle bin is enabled, dropped tables and their dependent objects are placed in the recycle bin. When the recycle bin is disabled, dropped tables and their dependent objects are not placed in the recycle bin; they are just dropped, and you must use other means to recover them (such as recovering from backup).
The recycle bin is enabled by default.
To disable the recycle bin:
Issue one of the following statements:
ALTER SESSION SET recyclebin = OFF; ALTER SYSTEM SET recyclebin = OFF;
To enable the recycle bin:
Issue one of the following statements:
ALTER SESSION SET recyclebin = ON; ALTER SYSTEM SET recyclebin = ON;
Enabling and disabling the recycle bin with an
ALTER SYSTEM or
ALTER SESSION statement takes effect immediately. Disabling the recycle bin does not purge or otherwise affect objects already in the recycle bin.
Like any other initialization parameter, you can set the initial value of the
recyclebin parameter in the text initialization file
See Also:"About Initialization Parameters and Initialization Parameter Files" for more information on initialization parameters.
||This view can be used by users to see their own dropped objects in the recycle bin. It has a synonym
||This view gives administrators visibility to all dropped 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:
SELECT object_name, original_name FROM dba_recyclebin WHERE owner = 'HR'; OBJECT_NAME ORIGINAL_NAME ------------------------------ -------------------------------- BIN$yrMKlZaLMhfgNAgAIMenRA==$0 EMPLOYEES
You can also view the contents of the recycle bin using the SQL*Plus command
SQL> show recyclebin ORIGINAL NAME RECYCLEBIN NAME OBJECT TYPE DROP TIME ---------------- ------------------------------ ------------ ------------------- EMPLOYEES BIN$yrMKlZaVMhfgNAgAIMenRA==$0 TABLE 2003-10-27:14:00:19
You can query objects that are in the recycle bin, just as you can query other objects. However, you must specify the name of the object as it is identified in the recycle bin. For example:
SELECT * FROM "BIN$yrMKlZaVMhfgNAgAIMenRA==$0";
If you decide that you are never going to restore an item from the recycle bin, you can use the
PURGE statement to remove the items and their associated objects from the recycle bin and release their storage space. You need the same privileges as if you were dropping the item.
When you use the
PURGE statement to purge a table, you can use the name that the table is known by in the recycle bin or the original name of the table. The recycle bin name can be obtained from either the
USER_RECYCLEBIN view as shown in "Viewing and Querying Objects in the Recycle Bin". The following hypothetical example purges the table
hr.int_admin_emp, which was renamed to
BIN$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:
PURGE TABLESPACE example; PURGE TABLESPACE example USER oe;
Users can purge the recycle bin of their own objects, and release space for objects, by using the following statement:
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.
See Also:Oracle Database SQL Language Reference for more information on the
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
USER_RECYCLEBIN view as shown in "Viewing and Querying Objects in the Recycle Bin". To use the
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:
FLASHBACK TABLE int_admin_emp TO BEFORE DROP RENAME TO int2_admin_emp;
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. Including the create time in the query can help you verify that you are restoring the correct table.
SELECT object_name, original_name, createtime FROM recyclebin; OBJECT_NAME ORIGINAL_NAME CREATETIME ------------------------------ --------------- ------------------- BIN$yrMKlZaLMhfgNAgAIMenRA==$0 INT2_ADMIN_EMP 2006-02-05:21:05:52 BIN$yrMKlZaVMhfgNAgAIMenRA==$0 INT2_ADMIN_EMP 2006-02-05:21:25:13 BIN$yrMKlZaQMhfgNAgAIMenRA==$0 INT2_ADMIN_EMP 2006-02-05:22:05:53 FLASHBACK TABLE BIN$yrMKlZaVMhfgNAgAIMenRA==$0 TO BEFORE DROP;
When you restore a table from the recycle bin, dependent objects such as indexes do not get their original names back; they retain their system-generated recycle bin names. You must manually rename dependent objects if you want to restore their original names. If you plan to manually restore original names for dependent objects, ensure that you make note of each dependent object's system-generated recycle bin name before you restore the table.
The following is an example of restoring the original names of some of the indexes of the dropped table
JOB_HISTORY, from the
HR sample schema. The example assumes that you are logged in as the
JOB_HISTORY and before restoring it from the recycle bin, run the following query:
SELECT OBJECT_NAME, ORIGINAL_NAME, TYPE FROM RECYCLEBIN; OBJECT_NAME ORIGINAL_NAME TYPE ------------------------------ ------------------------- -------- BIN$DBo9UChtZSbgQFeMiAdCcQ==$0 JHIST_JOB_IX INDEX BIN$DBo9UChuZSbgQFeMiAdCcQ==$0 JHIST_EMPLOYEE_IX INDEX BIN$DBo9UChvZSbgQFeMiAdCcQ==$0 JHIST_DEPARTMENT_IX INDEX BIN$DBo9UChwZSbgQFeMiAdCcQ==$0 JHIST_EMP_ID_ST_DATE_PK INDEX BIN$DBo9UChxZSbgQFeMiAdCcQ==$0 JOB_HISTORY TABLE
Restore the table with the following command:
FLASHBACK TABLE JOB_HISTORY TO BEFORE DROP;
Run the following query to verify that all
JOB_HISTORY indexes retained their system-generated recycle bin names:
SELECT INDEX_NAME FROM USER_INDEXES WHERE TABLE_NAME = 'JOB_HISTORY'; INDEX_NAME ------------------------------ BIN$DBo9UChwZSbgQFeMiAdCcQ==$0 BIN$DBo9UChtZSbgQFeMiAdCcQ==$0 BIN$DBo9UChuZSbgQFeMiAdCcQ==$0 BIN$DBo9UChvZSbgQFeMiAdCcQ==$0
Restore the original names of the first two indexes as follows:
ALTER INDEX "BIN$DBo9UChtZSbgQFeMiAdCcQ==$0" RENAME TO JHIST_JOB_IX; ALTER INDEX "BIN$DBo9UChuZSbgQFeMiAdCcQ==$0" RENAME TO JHIST_EMPLOYEE_IX;
Note that double quotes are required around the system-generated names.