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Step 9 - Restore and Recovery operations
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Learn Oracle - Restore and Recovery Operations
Restoring and recovering your whole database from a backup is completely
automated, thanks to the record of your existing backups kept in the RMAN
repository and the intelligence built into Recovery Manager. As long as Oracle DBA have
taken your backups through Recovery Manager (whether at the command line or
through Enterprise Manager), the entire restore and media recovery operation can be
performed through the Enterprise Manager.
To access the restore and recovery tasks, from the database home page, choose the
Maintenance property page, then under the heading Backup/Recovery choose
Perform Recovery to start the Recovery wizard.
On the Perform Recovery: Type page, in the Type field, select the type of restore
operation to perform. Oracle DBA can choose to recover a whole database or selected
tablespaces, datafiles, archived logs, or tables.
Recovering a Whole Database from Backup
On the Perform Recovery: Type page, set the Type to Whole Database. The Operation
Type drop-down menu will update to offer Oracle DBA the choices appropriate to a whole
database restore: restoring files only, recovery only, and both restoring and recovering
your database. Select Restore and Recover. Also, provide the requested host
credentials at this time if necessary and click Continue.
At this point, Oracle shuts down your database, and Oracle DBA arrive at a Database page
where Oracle DBA are given the opportunity to Startup or Perform Recovery. Choose
Perform Recovery.
After the database reaches the MOUNTED state, Enterprise Manager responds with a
page warning that the state of the database is unavailable (meaning that Enterprise
Manager cannot determine the state), but that the database may be in a NOMOUNT or
MOUNTED state. At this time Oracle DBA will be offered two choices: Startup and Perform
Recovery. Because you know that the database is down so that you can perform your
recovery, do not choose Startup. Click Perform Recovery to resume your recovery
session. You may be prompted for host and database credentials. Then Oracle DBA will reach
recovery of your database, the database state will be altered by
steps you take during the wizard. Changes, some of them
irrevocable, are made to your database at certain steps. For
example, the database may be shut down and brought to
MOUNTED state, or datafiles may be overwritten with versions
from backup.
Oracle Enterprise Manager will display warnings each time a
significant database change will result from pressing Continue
during the recovery process. Pay close attention to these warnings.
Note: The discussion which follows assumes that you are
restoring and recovering your database after the loss of one or more
datafiles, but still have a usable SPFILE and control file. Enterprise
Manager can also be used to restore a lost SPFILE or control file.
Enterprise Manager may respond with an
error page during the period when the database is being shut down
and brought to the MOUNTED state. Wait a while and refresh the
page until the error no longer occurs.
the Perform Recovery: Type page again, only now the database is in a MOUNTED
state (as is required for this operation) instead of being open. At this point, as you did
before, select Whole Database for Object Type and Restore and Recover for
Operation, and click Continue.
Next, Oracle DBA see the Perform Recovery: Credentials page, where you are again prompted
for operating system-level and Oracle database credentials. Provide these, and click
Continue to begin the recovery process.
In the first step of performing whole database recovery, Perform Recovery:Point in
Time, you specify whether to recover all transactions to your database as of the present
time (which is called complete recovery), or only transactions up through some point
in time in the past (which is called point-in-time recovery). Point-in-time recovery is
an advanced recovery technique that lets you return the database to its state before
some unwanted major change. For more details about point-in-time recovery, see
Oracle Database Backup and Recovery Advanced User's Guide. For this example, however,
recover the database to the current point in time. Click Continue after making your
selection.
In the next step, Perform Recovery: Rename, Oracle DBA can rename the files being restored
from backup. You can specify a new path for the files, restoring them to a different
directory. For this example, however, restore the files to the default location, which is
its location before the restore operation. Click Next to continue.
Finally, on the Perform Recovery: Review page, you can review the options you chose,
and view the RMAN script that will be run to carry out your requested restore and
recovery action. Click Submit to start the recovery process.
Recovering from a Lost SPFILE or Control File
The process for recovering a database with a lost SPFILE or control file is similar to
recovery of all datafiles. If Oracle DBA have lost a control file, your database is definitely
down. On attempting to start an Enterprise Manager session to your database, you
will encounter the warning that the database state is unavailable, and you must choose
between Startup and Perform Recovery. Because you do not know why your database
is down, click Startup. Enterprise Manager attempts to open the database. In the
process, it will detect a lost or unusable SPFILE or control file. If the startup fails,
choose Perform Recovery and Enterprise Manager will prompt Oracle DBA to restore the lost
files. If you are not using a recovery catalog, you will have to restore these files from
autobackup. You may
also need to provide Enterprise Manager the location where Oracle DBA directed control file
autobackups, which can be the location of the flash recovery area or some other
location on disk of your choosing.
Returning a Table to a Past State: Flashback Table
Oracle Flashback Table lets you revert one or more tables back to their contents at a
previous time, without affecting other objects in your database. This recovery
technique lets you recover from logical data corruptions, such as erroneously inserting
rows into a table or deleting data from a table. Flashback Table lets you return tables
Oracle DBA select to their state at a past point in time, without undoing desired changes to the
other objects in your database, as would be required by a point-in-time recovery of the
entire database. Also, unlike point-in-time recovery, your database remains available
during the operation.
For this example, we will perform Flashback Table on the EMPLOYEES table in the
HR schema. Assume that an erroneous update shortly after 23 October 2004, 15:30:00
has changed the LASTNAME column for all employees to an empty string and you
need to return the original LASTNAME values to the table.
Before you can perform Flashback Table, you must ensure that row movement is
enabled on the table to be flashed back.
Enabling Row Movement on a Table
To enable row movement, or if you do not know whether row movement is enabled,
follow these steps:
1. From the database home page, choose the Administration page. Then, under
Schema, click Tables to administer tables. To find the target table for flashback
table, you can enter one or both of the schema name in the Type field and the
table name in the Object Name field. Then click OK to search for the table. Oracle DBA
may need to page through the search results to find your table.
2. After you find your table in the schema, click the name of the table in the Table
Name column of the search results. Enterprise Manager displays a page with
several property pages for administering different aspects of the table. Select the
Options property page.
3. Make sure Enable Row Movement is set to Yes, and click Apply to update the
options for the table. When the page has refreshed, you can click Tables in the
breadcrumb at the top of the page to return to the search results, and enable row
movement on more tables by repeating these steps for each table.
Performing Flashback Table
To perform the Flashback Table operation, use the following steps:
1. From the Maintenance property page of the database home page, under the
Backup/Recovery heading, select Perform Recovery, and on the Perform
Recovery: Type page, select Tables for the object type. Choose the Flashback
Existing Tables option and click Continue.
2. On the Perform Recovery: Point-in-time page, you must choose the target time for
your Flashback Table operation. If you do not know the time at which the
unwanted changes occurred, you can investigate the history of transactions
affecting this table by choosing Evaluate row changes and transactions to decide
upon a point in time. A feature called Oracle Flashback Versions Query lets Oracle DBA
review all recent changes to the target table.
For this example, assume that the time of the corruption is known to be Oct. 3,
2004, 11:53AM. In the form offered, select Flashback to a timestamp, and enter
your target time. Click Next to continue with the Flashback Table process.
3. Now, on the Perform Recovery: Flashback Tables page, specify the target tables for
Flashback Table, by entering table names (one on each line) in the Tables to
Flashback text box. You can also click Add Tables and search for more tables to
add. For this example, manually enter the HR.EMPLOYEES table in the Tables to
Flashback text box. Click Next to continue with the Flashback Table process.
4. If your table has other dependent tables, you next see the Dependency Options
page, where you are asked how they should be handled. Your choices are Cascade
(flashing back any dependent tables), Restrict (flashing back only the target table),
or Customize (selecting which dependent tables to flashback and which to leave
as they are). You can click Show Dependencies to see which tables will be
affected. How you proceed at this point will depend upon your application.
HR.EMPLOYEES has dependent tables HR.JOBS and HR.DEPARTMENTS. For
this example, assume that it is safe to cascade any changes, flashing back those
two tables as well as the HR.EMPLOYEES table. Note that row movement must be
enabled on all affected tables, not just the initial target table. Click Next to
continue. The next page to appear is the Perform Recovery: Review page, where
Oracle DBA have a chance to confirm the Flashback Table operation to be performed. The
target timestamp and tables to be flashed back are displayed. Click Submit to
perform the actual Flashback Table operation. When the operation is completed, a
Confirmation page appears announcing the results. Click OK to return to the
database home page.
Recovering Dropped Tables: Flashback Drop
Oracle Flashback Drop lets you reverse the effects of dropping a table, returning the
dropped table to the database along with its dependent objects such as indexes and
triggers. It works by storing dropped objects in a Recycle Bin, from which they may be
retrieved until the Recycle Bin is purged, either explicitly or because space is needed
for new database objects.
As with Flashback Table, Flashback Drop can be used while the rest of your database
remains open, and without undoing desired changes in objects not affected by the
Flashback Drop operation. It is more convenient than forms of recovery that require
taking the database offline and restoring files from backup.
Follow these steps to perform Flashback Drop:
1. From the Maintenance property page of the database home page, under the
Backup/Recovery heading, select Perform Recovery, and on the Perform
Recovery: Type page, select Tables for the object type. For the Operation Type,
choose Flashback dropped tables. Then click Continue. This takes you to the
Perform Recovery: Dropped Objects Selection page.
2. On the Perform Recovery: Dropped Objects Selection page, you can gain access to
the objects in the Recycle Bin. The Search form lets you search among the dropped
objects in the Recycle Bin for the objects you want to recover. Provide values for
one or both of the Schema Name and Table fields, and click Go to search.
When the page refreshes, the Results section lists the objects matching your search.
If you only see the Recycle Bin listed, click the arrow next to the Recycle Bin to
expand its contents by one level, showing dropped tables matching your search
but not their dependent objects. You can also click Expand All to see all objects in
the Recycle Bin, including both dropped tables and dependent objects such as
indexes and triggers. For each table listed, Oracle DBA can click View Content in the
Operation column, to see its contents.
To select one or more tables for Flashback Drop, click the checkbox next to each
table. (When a table is retrieved from the Recycle Bin, all of the dependent objects
for the table that are in the recycle bin are brought back as well. They cannot be
retrieved separately.) When you have selected all of your objects to restore, click
Next.
Note: For a table to be recoverable using Flashback Drop, it must
reside in a locally managed tablespace. Also, tables in the SYSTEM
tablespaces cannot recovered using Flashback Drop regardless of
the tablespace type.
3. On the Perform Recovery: Rename page, you have the opportunity to specify new
names for any dropped objects you are returning to your database. The primary
reason for renaming objects being retrieved from the recycle bin is if you have
created new tables with the same names as tables being retrieved. Enter new
names as needed in the New Name field in the list of tables being flashed back.
Then click Next to continue.
4. On the Perform Recovery: Review page, you are offered an impact analysis,
showing the full set of objects to be flashed back, including the dependent objects,
as well as the names they will have when the Flashback Drop operation is
complete. If Oracle DBA are satisfied with the changes listed, click Submit to perform the
Flashback Drop.
When the process is complete, you arrive at a confirmation page indicating the success
of the operation. Click OK to return to the database home page.
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