Databases Reference
In-Depth Information
In all of these situations, you can use either point-in-time recovery or Oracle's flashback technology to get the
database back to a previous point in time. Prior to the introduction of the flashback technology, a database point-
in-time recovery (DBPITR) and a tablespace point-in-time recovery (TSPITR) were the automatic solutions when
confronted by situations such as an erroneous data entry or wrong updates. Flashback technology offers you the
capability to perform point-in-time recovery much quicker than the traditional point-in-time recovery techniques
that rely on media recovery. The flashback database feature is the alternative to traditional database point-in-time
recovery, while the flashback table feature lets you avoid having to perform a media recovery in most cases.
Deciding on the Appropriate Recovery Technique
Fortunately for Oracle database administrators, several recovery techniques are available, such as media recovery,
Oracle flashback, and so on, each geared toward recovering from a certain type of problem. Here's a summary of when
to use the various types of recovery techniques:
•
Use media recovery if you're confronted with damaged, missing, or inaccessible data files.
•
If a user drops a table or commits a major data entry error, you can perform a point-in-time
media recovery, but the best option is to use the
flashback drop
feature. You can also import
the affected table using the Data Pump Import utility or have users reenter data in some
situations. You can also use the RMAN command
recover table
, which is a brand-new
Oracle Database 12c feature.
•
If you run into logical errors, perform a TSPITR or consider using an appropriate flashback
technique to make a point-in-time recovery.
•
If you have data corruption in a few blocks in a data file or a set of data files, use block media
recovery. Again, there's no need to perform a media recovery and make the rest of the
database inaccessible.
•
If a user error affects a large set of tables or the entire database, use the flashback database
feature to revert the database to a previous “good” time by undoing all the changes since that
point in time.
•
Use the flashback table feature to revert to a previous state of a table in order to undo
unwanted changes. Starting with Oracle Database 12c, you can also use the RMAN recover
table command to recover a table to a specified point in time.
RMAN Architecture
You can start performing backups with RMAN without installing or configuring a thing. Simply invoke the RMAN
client by using the RMAN executable (named
rman
) from the $ORACLE_HOME/bin directory, and you're ready to go.
Just specify the target database you want to work with at the command line, and that's it. You can perform backup and
recovery actions with RMAN through the RMAN client or through the Enterprise Manager GUI.
In addition to the RMAN client, you may use additional optional components to make your backup and recovery
strategy robust and easy:
The recovery catalog
: The target database control file will always store the RMAN repository,
which is the set of RMAN-related backup and recovery information. This data is also
referred to as RMAN's
metadata
. However, it's smarter to use a dedicated database to store
the RMAN repository. You can then create a special schema called the
recovery catalog
in
this dedicated database and have RMAN store its repository in it, thus avoiding the risk of
the critical metadata being overwritten when the control file runs out of space. As you'll see
in Chapter 6, using a recovery catalog, which is optional, has several other advantages.
