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Mouhamadou Diaw

Oracle 12.2 Dataguard : PDB Flashback on the Primary

The last day I was discussing with one colleague about database flashback for a pluggable database in a dataguard environment. I did some tests and I present results in this blog.
Below our broker configuration. Oracle 12.2 is used.

DGMGRL> show configuration;
Configuration - MYCONT_DR
Protection Mode: MaxPerformance
Members:
MYCONT_SITE - Primary database
MYCONT_SITE1 - Physical standby database
Fast-Start Failover: DISABLED
Configuration Status:
SUCCESS (status updated 35 seconds ago)
DGMGRL>

The primary database has the flashback database set to YES.

SQL> select db_unique_name,open_mode,flashback_on from v$database;
DB_UNIQUE_NAME OPEN_MODE FLASHBACK_ON
------------------------------ -------------------- ------------------
MYCONT_SITE READ WRITE YES
.
SQL> select name,open_mode from v$pdbs;
NAME OPEN_MODE
-------------------- ----------
PDB$SEED READ ONLY
PDB1 READ WRITE
PDB2 READ WRITE

Same for the standby database

SQL> select db_unique_name,open_mode,flashback_on from v$database;
DB_UNIQUE_NAME OPEN_MODE FLASHBACK_ON
------------------------------ -------------------- ------------------
MYCONT_SITE1 READ ONLY WITH APPLY YES
.
SQL> select name,open_mode from v$pdbs;
NAME OPEN_MODE
-------------------- ----------
PDB$SEED READ ONLY
PDB1 READ ONLY
PDB2 READ ONLY

For the tests we are going to do a flashback database for the primary PDB1.
Let’s connect to PDB1

10:15:59 SQL> alter session set container=pdb1;
Session altered.
.
10:16:15 SQL> show con_name;
CON_NAME
------------------------------
PDB1
10:16:22 SQL>

And let’s create a table article with some datafor reference

10:16:22 SQL> create table article (idart number);
Table created.
.
10:18:12 SQL> insert into article values (1);
1 row created.
10:18:31 SQL> insert into article values (2);
1 row created.
.
10:18:34 SQL> select * from article;
IDART
----------
1
2
.
10:18:46 SQL> commit;

Now let’s do a database flashback of primary pdb1 before the creation of the table article.

10:28:12 SQL> show con_name
CON_NAME
------------------------------
PDB1
.
10:28:16 SQL> shut immediate;
Pluggable Database closed.
.
10:28:28 SQL> select name,open_mode from v$pdbs;
NAME OPEN_MODE
-------------------- ----------
PDB1 MOUNTED
10:28:54 SQL>
.
10:28:54 SQL> FLASHBACK PLUGGABLE DATABASE PDB1 TO TIMESTAMP TO_TIMESTAMP('2017-12-20 10:16:00', 'YYYY-MM-DD HH24:MI:SS');
Flashback complete.
10:30:14 SQL>

Now let’s open PDB1 with resetlogs option

10:31:08 SQL> alter pluggable database PDB1 open resetlogs;
Pluggable database altered.
10:32:15 SQL>

And let’s query the table article. As expected the table is no longer present

10:32:15 SQL> select name,open_mode from v$pdbs;
NAME OPEN_MODE
-------------------- ----------
PDB1 READ WRITE
.
10:32:59 SQL> select * from article;
select * from article
*
ERROR at line 1:
ORA-00942: table or view does not exist
10:33:06 SQL>

Now if we check the status of our dataguard in the broker, we have errors

12/20/2017 10:23:07 DGMGRL> show configuration;
Configuration - MYCONT_DR
Protection Mode: MaxPerformance
Members:
MYCONT_SITE - Primary database
MYCONT_SITE1 - Physical standby database
Error: ORA-16810: multiple errors or warnings detected for the member
Fast-Start Failover: DISABLED
Configuration Status:
ERROR (status updated 48 seconds ago)
12/20/2017 10:34:40 DGMGRL>

The status of the Primary database is fine

12/20/2017 10:34:40 DGMGRL> show database 'MYCONT_SITE';
Database - MYCONT_SITE
Role: PRIMARY
Intended State: TRANSPORT-ON
Instance(s):
MYCONT
Database Status:
SUCCESS

But the standby status is returning some errors
12/20/2017 10:35:11 DGMGRL> show database 'MYCONT_SITE1';
Database - MYCONT_SITE1
Role: PHYSICAL STANDBY
Intended State: APPLY-ON
Transport Lag: 0 seconds (computed 1 second ago)
Apply Lag: 3 minutes 10 seconds (computed 1 second ago)
Average Apply Rate: 7.00 KByte/s
Real Time Query: OFF
Instance(s):
MYCONT
Database Error(s):
ORA-16766: Redo Apply is stopped
Database Warning(s):
ORA-16853: apply lag has exceeded specified threshold
Database Status:
ERROR
12/20/2017 10:35:15 DGMGRL>

And if we check the alert log of the standby dataset we can find following errors

(3):Recovery of pluggable database PDB1 aborted due to pluggable database open resetlog marker.
(3):To continue recovery, restore all data files for this PDB to checkpoint SCN lower than 2518041, or timestamp before 12/20/2017 10:16:01, and restart recovery
MRP0: Background Media Recovery terminated with error 39874
2017-12-20T10:32:05.565085+01:00
Errors in file /u01/app/oracle/diag/rdbms/mycont_site1/MYCONT/trace/MYCONT_mrp0_1590.trc:
ORA-39874: Pluggable Database PDB1 recovery halted
ORA-39873: Restore all data files to a checkpoint SCN lower than 2518041.
Managed Standby Recovery not using Real Time Apply
Recovery interrupted!
Recovered data files to a consistent state at change 2520607
2017-12-20T10:32:05.612394+01:00
Errors in file /u01/app/oracle/diag/rdbms/mycont_site1/MYCONT/trace/MYCONT_mrp0_1590.trc:
ORA-39874: Pluggable Database PDB1 recovery halted
ORA-39873: Restore all data files to a checkpoint SCN lower than 2518041.
2017-12-20T10:32:05.612511+01:00
MRP0: Background Media Recovery process shutdown (MYCONT)

On the primary PDB, we can can query the current INCARNATION_SCN in the v$pdb_incarnation view. And we can remark that the current SCN is the same that the one specified in the standby alert log 2518041

11:08:11 SQL> show con_name
CON_NAME
------------------------------
PDB1
11:08:56 SQL> select status,INCARNATION_SCN from v$pdb_incarnation;
STATUS INCARNATION_SCN
------- ---------------
CURRENT 2518041
PARENT 2201909
PARENT 1396169
11:08:59 SQL>

And then as specified in the alert log we have to flashback the standby pdb to a SCN lower than 2518041
First let’s stop the redo apply on the standby

12/20/2017 11:13:14 DGMGRL> edit database 'MYCONT_SITE1' set state='APPLY-OFF';
Succeeded.
12/20/2017 11:13:59 DGMGRL>

And then let’s flashback to 2518039 ( i.e 2518041 -2 ) for example
Let’s shutdown the standby container MYCONT and startup it in a mount state

11:18:42 SQL> shut immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
.
11:19:10 SQL> startup mount
ORACLE instance started.
Total System Global Area 956301312 bytes
Fixed Size 8799656 bytes
Variable Size 348129880 bytes
Database Buffers 595591168 bytes
Redo Buffers 3780608 bytes
Database mounted.
11:19:50 SQL>
.
11:19:50 SQL> select name,open_mode from v$pdbs;
NAME OPEN_MODE
-------------------- ----------
PDB$SEED MOUNTED
PDB1 MOUNTED
PDB2 MOUNTED

Now let’s flashback PDB1 on the standby

11:20:19 SQL> flashback pluggable database PDB1 to SCN 2518039;
Flashback complete.
11:20:40 SQL>

The last step is to enable again the redo apply for the standby container

12/20/2017 11:13:59 DGMGRL> edit database 'MYCONT_SITE1' set state='APPLY-ON';
Succeeded.
12/20/2017 11:23:08 DGMGRL>

And then we can verify that the configuration is now fine

12/20/2017 11:25:05 DGMGRL> show configuration;
Configuration - MYCONT_DR
Protection Mode: MaxPerformance
Members:
MYCONT_SITE - Primary database
MYCONT_SITE1 - Physical standby database
Fast-Start Failover: DISABLED
Configuration Status:
SUCCESS (status updated 1 second ago)
12/20/2017 11:25:07 DGMGRL>

Conclusion
In this article we saw that the flashback in a dataguard environment is working in the same way for a container or a non container. The only difference is the SCN we must consider to flashback the pluggable database. This SCN should be queried fom the v$pdb_incarnation and not from the v$database as we usually do for a non container database.

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Mouhamadou Diaw
Mouhamadou Diaw

Consultant