Database Reference
In-Depth Information
Recovery of the UNDO Tablespace
There are cases where the
UNDO
tablespace can be recovered online. If the database was
shut down in a consistent manner before the
UNDO
tablespace was lost, it may be that all
you will need to do is take the
UNDO
tablespace data files offline (you won't be able to take
the tablespace itself offline) and then open the database.
Oracle has a default
SYSTEM
tablespace that would be used in this case, when the data-
base initially comes up. You could then just create a new
UNDO
tablespace and drop the
old one. This might be a quicker recovery method in some cases.
Recovering the Database after the Loss of One or More
Non-SYSTEM or -UNDO Tablespace Data Files
If the tablespace/data file you lost is not associated with the
SYSTEM
or
UNDO
tablespaces, then
you are in luck. You don't even need to shut down the database to recover! All you need to
do is take the data files offline, restore the impacted data files, recover the data files (or the
tablespace), and bring them back online.
The nice thing about this is if your users are not using the tablespace, they will never
know there was a problem. If the users are using the tablespace, they will be impacted only
if they try to use the data files that are offline (which is one good reason in some cases to
take just the data files offline rather than the whole tablespace).
The first question is, how do you know which data files are missing? There are a couple
of things that will give you a clue. First of all, your users will start getting these messages:
SQL> select * from scott.emp;
select * from scott.emp
*
ERROR at line 1:
ORA-00376: file 4 cannot be read at this time
ORA-01110: data file 4: 'C:\ORACLE\ORADATA\ORCL\USERS01.DBF'
You can also look at the
V$RECOVER_FILE
view for more information on data files that
need recovery. Here is an example of such a query:
SQL> select file#, 'online', online_status, error from v$recover_file;
FILE# ONLINE ONLINE_ ERROR
---------- ------- ------- -------------------- ---------- ---------
4 ONLINE ONLINE FILE NOT FOUND
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