12c: How to Restore/Recover a Small Table in a Large Database

Aug 28, 2014 / By Howie Jiang

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As a DBA, you will receive requests from developers or users, indicating that they deleted some data in a small table in a large database a few hours prior. They will probably want you to recover the data as soon as possible, and it will likely be a critical production database. Flashback will not be enabled, and the recycle bin will have been purged. Restoring a full database using RMAN might take you over 10 hours, and you will need a spare server with big storage. Looks like it’s going to be a difficult and time consuming task for you.

In Oracle Database 12c, there is a method available which allows us to recover the table more efficiently, and at a lower cost. The method is to create a second database (often called a stub database) using the backup of the first database. In this situation, we restore the SYSTEM, SYSAUX, and UNDO tablespaces and the the individual tablespaces that contain the data that we want to restore. After the restore is complete, we alter any tablespaces that we did not restore offline. We then apply the archived redo logs to the point in time that we want to restore the table to. Having restored the database to the appropriate point in time, we then use Oracle Data Pump to export the objects, and then you import them into the original database, again using Oracle Data Pump. Oracle Database 12c introduces new functionality in RMAN that supports point-in-time restore of individual database tables and individual table partitions.

Here is an example of when I tested this new feature:

1. The database TEST has 9 tablespaces and a schema called Howie. I created a table with 19377 records called TEST1 which is in the tablespace DATA_HOWIE.

SQL> select * from v$instance;

INSTANCE_NUMBER INSTANCE_NAME    HOST_NAME                                                        VERSION           STARTUP_T STATUS       PAR    THREAD# ARCHIVE LOG_SWITCH_WAIT LOGINS     SHU DATABASE_STATUS   INSTANCE_ROLE      ACTIVE_ST BLO  CON_ID INSTANCE_MO EDITION FAMILY
--------------- ---------------- ---------------------------------------------------------------- ----------------- --------- ------------ --- ---------- ------- --------------- ---------- --- ----------------- ------------------ --------- --- ---------- ----------- ------- --------------------------------------------------------------------------------
1 TEST             12cServer1                                                       12.1.0.1.0        17-AUG-14 OPEN         NO           1 STARTED                 ALLOWED    NO  ACTIVE            PRIMARY_INSTANCE   NORMALNO            0 REGULAR     EE

SQL> select tablespace_name from dba_tablespaces order by tablespace_name;

TABLESPACE_NAME
------------------------------
DATA_HOWIE
DATA_TB1
DATA_TB2
DATA_TB3
SYSAUX
SYSTEM
TEMP
UNDOTBS1
USERS

9 rows selected.

SQL> conn howie
Enter password:
Connected.
SQL> create table test1 as select * from dba_objects;

Table created.

SQL> select count(*) from test1;

COUNT(*)
----------
19377

SQL> select table_name,tablespace_name from user_tables where table_name='TEST1';

TABLE_NAME                                                                                                                       TABLESPACE_NAME
-------------------------------------------------------------------------------------------------------------------------------- ------------------------------
TEST1                                                                                                                            DATA_HOWIE

2. The database is in archivelog mode, and I took a full backup of the database.

[oracle@12cServer1 RMAN]$ rman target /

Recovery Manager: Release 12.1.0.1.0 - Production on Sun Aug 17 20:16:17 2014

Copyright (c) 1982, 2013, Oracle and/or its affiliates.  All rights reserved.

connected to target database: TEST (DBID=2146502230)

RMAN> run
{
allocate channel d1 type disk format '/u01/app/oracle/RMAN/rmn_%d_t%t_p%p';
backup
incremental level 0
tag backup_level0
filesperset 1
(database)
plus archivelog ;
release channel d1;
}2> 3> 4> 5> 6> 7> 8> 9> 10> 11>

3. The data in the table howie.test1 has been deleted.

SQL> select sysdate,current_scn from v$database;

SYSDATE             CURRENT_SCN
------------------- -----------
08/17/2014 21:01:15      435599

SQL> delete test1;

19377 rows deleted.

SQL> commit;

Commit complete.

4. I ran following scripts to recover the data to an alternative table howie.test1_temp to the point in time “08/17/2014 21:01:15″

[oracle@12cServer1 RMAN]$ rman target /

Recovery Manager: Release 12.1.0.1.0 - Production on Sun Aug 17 21:01:35 2014

Copyright (c) 1982, 2013, Oracle and/or its affiliates.  All rights reserved.

connected to target database: TEST (DBID=2146502230)

RMAN> recover table howie.test1
until time "to_date('08/17/2014 21:01:15','mm/dd/yyyy hh24:mi:ss')"
auxiliary destination '/u01/app/oracle/aux'
remap table howie.test1:test1_temp;2> 3> 4>

5. The scripts above will take care of everything and you will see the data has been restored to howie.test1_temp

SQL> select count(*) from TEST1_TEMP;

COUNT(*)
----------
19377

SQL> select count(*) from TEST1;

COUNT(*)
----------
0

Let’s take a look at the log of RMAN recovery and find out how it works.

1. Creation of the auxiliary instance

Creating automatic instance, with SID='ktDA'

initialization parameters used for automatic instance:
db_name=TEST
db_unique_name=ktDA_pitr_TEST
compatible=12.1.0.0.0
db_block_size=8192
db_files=200
sga_target=1G
processes=80
diagnostic_dest=/u01/app/oracle
db_create_file_dest=/u01/app/oracle/aux
log_archive_dest_1='location=/u01/app/oracle/aux'
#No auxiliary parameter file used

2. Restore of the control file for the auxiliary instance

contents of Memory Script:
{
# set requested point in time
set until  time "to_date('08/17/2014 21:01:15','mm/dd/yyyy hh24:mi:ss')";
# restore the controlfile
restore clone controlfile;
# mount the controlfile
sql clone 'alter database mount clone database';
# archive current online log
sql 'alter system archive log current';
}

3. A list of datafiles that will be restored, followed by their restore and recovery in the auxiliary instance

contents of Memory Script:
{
# set requested point in time
set until  time "to_date('08/17/2014 21:01:15','mm/dd/yyyy hh24:mi:ss')";
# online the datafiles restored or switched
sql clone "alter database datafile  1 online";
sql clone "alter database datafile  3 online";
sql clone "alter database datafile  2 online";
# recover and open database read only
recover clone database tablespace  "SYSTEM", "UNDOTBS1", "SYSAUX";
sql clone 'alter database open read only';
}

contents of Memory Script:
{
# set requested point in time
set until  time "to_date('08/17/2014 21:01:15','mm/dd/yyyy hh24:mi:ss')";
# online the datafiles restored or switched
sql clone "alter database datafile  8 online";
# recover and open resetlogs
recover clone database tablespace  "DATA_HOWIE", "SYSTEM", "UNDOTBS1", "SYSAUX" delete archivelog;
alter clone database open resetlogs;
}

4. Export of tables from the auxiliary instance via Oracle Data Pump

Performing export of tables...
EXPDP> Starting "SYS"."TSPITR_EXP_ktDA_BAkw":
EXPDP> Estimate in progress using BLOCKS method...
EXPDP> Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
EXPDP> Total estimation using BLOCKS method: 3 MB
EXPDP> Processing object type TABLE_EXPORT/TABLE/TABLE
EXPDP> Processing object type TABLE_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
EXPDP> Processing object type TABLE_EXPORT/TABLE/STATISTICS/MARKER
EXPDP> . . exported "HOWIE"."TEST1"                             1.922 MB   19377 rows
EXPDP> Master table "SYS"."TSPITR_EXP_ktDA_BAkw" successfully loaded/unloaded
EXPDP> ******************************************************************************
EXPDP> Dump file set for SYS.TSPITR_EXP_ktDA_BAkw is:
EXPDP>   /u01/app/oracle/aux/tspitr_ktDA_70244.dmp
EXPDP> Job "SYS"."TSPITR_EXP_ktDA_BAkw" successfully completed at Sun Aug 17 21:03:53 2014 elapsed 0 00:00:14
Export completed

5. Import of tables, constraints, indexes, and other dependent objects into the target database from the Data Pump export file

contents of Memory Script:
{
# shutdown clone before import
shutdown clone abort
}
executing Memory Script

Oracle instance shut down

Performing import of tables...
IMPDP> Master table "SYS"."TSPITR_IMP_ktDA_lube" successfully loaded/unloaded
IMPDP> Starting "SYS"."TSPITR_IMP_ktDA_lube":
IMPDP> Processing object type TABLE_EXPORT/TABLE/TABLE
IMPDP> Processing object type TABLE_EXPORT/TABLE/TABLE_DATA
IMPDP> . . imported "HOWIE"."TEST1_TEMP"                        1.922 MB   19377 rows
IMPDP> Processing object type TABLE_EXPORT/TABLE/STATISTICS/TABLE_STATISTICS
IMPDP> Processing object type TABLE_EXPORT/TABLE/STATISTICS/MARKER
IMPDP> Job "SYS"."TSPITR_IMP_ktDA_lube" successfully completed at Sun Aug 17 21:04:19 2014 elapsed 0 00:00:19
Import completed

6. Clean-up of the auxiliary instance

Removing automatic instance
Automatic instance removed
auxiliary instance file /u01/app/oracle/aux/TEST/datafile/o1_mf_temp_9z2yqst6_.tmp deleted
auxiliary instance file /u01/app/oracle/aux/KTDA_PITR_TEST/onlinelog/o1_mf_3_9z2yrkqm_.log deleted
auxiliary instance file /u01/app/oracle/aux/KTDA_PITR_TEST/onlinelog/o1_mf_2_9z2yrj35_.log deleted
auxiliary instance file /u01/app/oracle/aux/KTDA_PITR_TEST/onlinelog/o1_mf_1_9z2yrh2r_.log deleted
auxiliary instance file /u01/app/oracle/aux/KTDA_PITR_TEST/datafile/o1_mf_data_how_9z2yrcnq_.dbf deleted
auxiliary instance file /u01/app/oracle/aux/TEST/datafile/o1_mf_sysaux_9z2yptms_.dbf deleted
auxiliary instance file /u01/app/oracle/aux/TEST/datafile/o1_mf_undotbs1_9z2yq9of_.dbf deleted
auxiliary instance file /u01/app/oracle/aux/TEST/datafile/o1_mf_system_9z2yp0mk_.dbf deleted
auxiliary instance file /u01/app/oracle/aux/TEST/controlfile/o1_mf_9z2yos1l_.ctl deleted
auxiliary instance file tspitr_ktDA_70244.dmp deleted
Finished recover at 17-AUG-14

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