Recovery of Missing undo datafile from coldbackup

Recovery of lost Undo Datafile

Hi All,

This blog is about strange experience I had during the restoration of database from cold backup.

I am working on R12 Upgrade project and as part of DBA Upgrade activity I took cold backup of complete database and application at the initial state of upgrade. Customer has provided us cifs file system to store our backups and it is somewhat different to the normal unix file system. This file system is not case sensitive and it is replacing the files with the same name but with different case and thus resulting in some loss of files. Luckily/Unlucky in my current database I have UNDO Tablespace with 3 data files and out of these two data files have same name with different case and thus when I took a complete cold backup of database resulting in loss of data file.

Now I had to use this backup for building another database and during recovery I found that one of the data files and when I investigated I could identify that the undo data file 1 is replaced by undo data file 2. So, As this is an undo data file I know that it doesn't contain user/system data(database shutdown is graceful) and losing it doesn't lose any of our data. Thus this gave us scenario of recovering database due to loss of undo data file.

This cold backup can be helpful only if the database is shutdown gracefully else the backup would be vane and I need to find another source of backup for restoration. As this is cold backup I could go ahead in recreating the lost undo data file and recover the database successfully.

Below is the procedure followed to restore the UNDO tablespace:

1) Verified the data files in backup location and showed that both files are existing

                [oratacrw@aoccol-101 CRP1Backup]$ pwd

                /mnt/R12_Backups/CRP1Backup

                [oratacrw@aoccol-101 CRP1Backup]$ ls -lrt APPS_UNDOTS1_2.DBF

                -rwxrwSrwt  1 root root 2097160192 Aug 26 11:02 APPS_UNDOTS1_2.DBF

                [oratacrw@aoccol-101 CRP1Backup]$ ls -lrt APPS_UNDOTS1_2*

                -rwxrwxrwx  1 oratacrw dba 2097160192 Aug 26 11:02 APPS_UNDOTS1_2.dbf

2) Copy all the data files from backup location to data files location

3) Modified the init parameters as per new db_name and also changed below parameters for disabling auto undo management.

                UNDO_MANAGEMENT=MANUAL

                The above setting makes database to use SYSTEM as undo tablespace instead of using actual undo tablespace(by default)

4) Create spfile from modified pfile;

                SQL> create spfile from pfile;     

5) Recreate control file manually and shutdown the database.

6) Mount the database in restricted mode.

                SQL> STARTUP RESTRICT MOUNT

                ORACLE instance started.

                Total System Global Area 1073741824 bytes

                Fixed Size                  2089336 bytes

                Variable Size             427822728 bytes

                Database Buffers          629145600 bytes

                Redo Buffers               14684160 bytes

                Database mounted.

7) Offline drop the missing undo data file from database and open the database.

                SQL> ALTER DATABASE DATAFILE '/u02/tacprefdata/APPS_UNDOTS1_01.dbf' OFFLINE DROP;

                Database altered.

                SQL> alter database open;

                Database altered.

8) Drop complete undo tablespace including datafiles.

                SQL> DROP TABLESPACE APPS_UNDOTS1 INCLUDING CONTENTS;

                Tablespace dropped.

               

9) Recreate the undo tablespace with required datafiles.

                SQL> CREATE UNDO TABLESPACE APPS_UNDOTS1 DATAFILE '/u02/tacprefdata/APPS_UNDOTS1_01.dbf' size 2G REUSE;

                Tablespace created.

10) shutdown the database and modify UNDO_MANAGEMENT parameter to "AUTO" and UNDO_TABLESPACE to "new undo ts"              

                SQL> shutdown immediate;

                Database closed.

                Database dismounted.

                ORACLE instance shut down.

               

                Init parameters

               

                undo_management = AUTO

                undo_tablespace = APPS_UNDOTS1

               

11) Recreate spfile and bring up the database

               

                SQL> create spfile from pfile;

                File created.

                SQL> startup

                ORACLE instance started.

                Total System Global Area 1073741824 bytes

                Fixed Size                  2089336 bytes

                Variable Size             427822728 bytes

                Database Buffers          629145600 bytes

                Redo Buffers               14684160 bytes

                Database mounted.

                Database opened

               

                SQL> sho parameter undo

                NAME                                 TYPE        VALUE

                ------------------------------------ ----------- ------------------------------

                undo_management                      string      AUTO

                undo_retention                       integer     900

                undo_tablespace                      string      APPS_UNDOTS1

               

Now the database is up and completely operational.

Thank you.