Data Guard Physical Standby Setup in Oracle Database 11g Release 2
Data Guard is the name for Oracle's standby database solution, used for disaster recovery and high availability. This article contains an updated version of the 9i physical standby setup method posted
here.
Related articles.
Assumptions
- You have two servers (physical or VMs) with an operating system and Oracle installed on them. In this case I've used Oracle Linux 5.6 and Oracle Database 11.2.0.2.
- The primary server has a running instance.
- The standby server has a software only installation.
Primary Server Setup
Logging
Check that the primary database is in archivelog mode.
SELECT log_mode FROM v$database;
LOG_MODE
------------
NOARCHIVELOG
SQL>
If it is noarchivelog mode, switch is to archivelog mode.
SHUTDOWN IMMEDIATE;
STARTUP MOUNT;
ALTER DATABASE ARCHIVELOG;
ALTER DATABASE OPEN;
Enabled forced logging by issuing the following command.
ALTER DATABASE FORCE LOGGING;
Initialization Parameters
Check the setting for the
DB_NAME and
DB_UNIQUE_NAME parameters. In this case they are both set to "DB11G" on the primary database.
SQL> show parameter db_name
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_name string DB11G
SQL> show parameter db_unique_name
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_unique_name string DB11G
SQL>
The
DB_NAME of the standby database will be the same as that of the primary, but it must have a different
DB_UNIQUE_NAME value. The
DB_UNIQUE_NAME values of the primary and standby database should be used in the
DG_CONFIG setting of the
LOG_ARCHIVE_CONFIG parameter. For this example, the standby database will have the value "DB11G_STBY".
ALTER SYSTEM SET LOG_ARCHIVE_CONFIG='DG_CONFIG=(DB11G,DB11G_STBY)';
Set suitable remote archive log destinations. In this case I'm using the fast recovery area for the local location, but you could specify an location explicitly if you prefer. Notice the
SERVICE and the
DB_UNIQUE_NAME for the remote location reference the standby location.
ALTER SYSTEM SET LOG_ARCHIVE_DEST_2='SERVICE=db11g_stby NOAFFIRM ASYNC VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=DB11G_STBY';
ALTER SYSTEM SET LOG_ARCHIVE_DEST_STATE_2=ENABLE;
The
LOG_ARCHIVE_FORMAT and
LOG_ARCHIVE_MAX_PROCESSES parameters must be set to appropriate values and the
REMOTE_LOGIN_PASSWORDFILE must be set to exclusive.
ALTER SYSTEM SET LOG_ARCHIVE_FORMAT='%t_%s_%r.arc' SCOPE=SPFILE;
ALTER SYSTEM SET LOG_ARCHIVE_MAX_PROCESSES=30;
ALTER SYSTEM SET REMOTE_LOGIN_PASSWORDFILE=EXCLUSIVE SCOPE=SPFILE;
In addition to the previous setting, it is recommended to make sure the primary is ready to switch roles to become a standby. For that to work properly we need to set the following parameters. Adjust the
*_CONVERT parameters to account for your filename and path differences between the servers.
ALTER SYSTEM SET FAL_SERVER=DB11G_STBY;
--ALTER SYSTEM SET DB_FILE_NAME_CONVERT='DB11G_STBY','DB11G' SCOPE=SPFILE;
--ALTER SYSTEM SET LOG_FILE_NAME_CONVERT='DB11G_STBY','DB11G' SCOPE=SPFILE;
ALTER SYSTEM SET STANDBY_FILE_MANAGEMENT=AUTO;
Remember, some of the parameters are not modifiable, so the database will need to be restarted before they take effect.
Service Setup
Entries for the primary and standby databases are needed in the "$ORACLE_HOME/network/admin/tnsnames.ora" files on both servers. You can create these using the Network Configuration Utility (netca) or manually. The following entries were used during this setup.
DB11G =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = ol5-112-dga1)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = DB11G.WORLD)
)
)
DB11G_STBY =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = ol5-112-dga2)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = DB11G.WORLD)
)
)
Backup Primary Database
If you are planning to use an active duplicate to create the standby database, then this step is unnecessary. For a backup-based duplicate, or a manual restore, take a backup of the primary database.
$ rman target=/
RMAN> BACKUP DATABASE PLUS ARCHIVELOG;
Create Standby Controlfile and PFILE
Create a controlfile for the standby database by issuing the following command on the primary database.
ALTER DATABASE CREATE STANDBY CONTROLFILE AS '/tmp/db11g_stby.ctl';
Create a parameter file for the standby database.
CREATE PFILE='/tmp/initDB11G_stby.ora' FROM SPFILE;
Amend the PFILE making the entries relevant for the standby database. I'm making a replica of the original server, so in my case I only had to amend the following parameters.
*.db_unique_name='DB11G_STBY'
*.fal_server='DB11G'
*.log_archive_dest_2='SERVICE=db11g ASYNC VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=DB11G'
Standby Server Setup (Manual)
Copy Files
Create the necessary directories on the standby server.
$ mkdir -p /u01/app/oracle/oradata/DB11G
$ mkdir -p /u01/app/oracle/fast_recovery_area/DB11G
$ mkdir -p /u01/app/oracle/admin/DB11G/adump
Copy the files from the primary to the standby server.
$ # Standby controlfile to all locations.
$ scp oracle@ol5-112-dga1:/tmp/db11g_stby.ctl /u01/app/oracle/oradata/DB11G/control01.ctl
$ cp /u01/app/oracle/oradata/DB11G/control01.ctl /u01/app/oracle/fast_recovery_area/DB11G/control02.ctl
$ # Archivelogs and backups
$ scp -r oracle@ol5-112-dga1:/u01/app/oracle/fast_recovery_area/DB11G/archivelog /u01/app/oracle/fast_recovery_area/DB11G
$ scp -r oracle@ol5-112-dga1:/u01/app/oracle/fast_recovery_area/DB11G/backupset /u01/app/oracle/fast_recovery_area/DB11G
$ # Parameter file.
$ scp oracle@ol5-112-dga1:/tmp/initDB11G_stby.ora /tmp/initDB11G_stby.ora
$ # Remote login password file.
$ scp oracle@ol5-112-dga1:$ORACLE_HOME/dbs/orapwDB11G $ORACLE_HOME/dbs
Notice, the backups were copied across to the standby server as part of the FRA copy. If your backups are not held within the FRA, you must make sure you copy them to the standby server and make them available from the same path as used on the primary server.
Start Listener
Make sure the listener is started on the standby server.
$ lsnrctl start
Restore Backup
Create the SPFILE form the amended PFILE.
$ export ORACLE_SID=DB11G
$ sqlplus / as sysdba
SQL> CREATE SPFILE FROM PFILE='/tmp/initDB11G_stby.ora';
Restore the backup files.
$ export ORACLE_SID=DB11G
$ rman target=/
RMAN> STARTUP MOUNT;
RMAN> RESTORE DATABASE;
Create Redo Logs
Create online redo logs for the standby. It's a good idea to match the configuration of the primary server.
ALTER SYSTEM SET STANDBY_FILE_MANAGEMENT=MANUAL;
ALTER DATABASE ADD LOGFILE ('/u01/app/oracle/oradata/DB11G/online_redo01.log') SIZE 50M;
ALTER DATABASE ADD LOGFILE ('/u01/app/oracle/oradata/DB11G/online_redo02.log') SIZE 50M;
ALTER DATABASE ADD LOGFILE ('/u01/app/oracle/oradata/DB11G/online_redo03.log') SIZE 50M;
ALTER SYSTEM SET STANDBY_FILE_MANAGEMENT=AUTO;
In addition to the online redo logs, you should create standby redo logs on both the standby and the primary database (in case of switchovers). The standby redo logs should be at least as big as the largest online redo log and there should be one extra group per thread compared the online redo logs. In my case, the following is standby redo logs must be created on both servers.
ALTER DATABASE ADD STANDBY LOGFILE ('/u01/app/oracle/oradata/DB11G/standby_redo01.log') SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE ('/u01/app/oracle/oradata/DB11G/standby_redo02.log') SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE ('/u01/app/oracle/oradata/DB11G/standby_redo03.log') SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE ('/u01/app/oracle/oradata/DB11G/standby_redo04.log') SIZE 50M;
Once this is complete, we can start the apply process.
Standby Server Setup (DUPLICATE)
Copy Files
Create the necessary directories on the standby server.
$ mkdir -p /u01/app/oracle/oradata/DB11G
$ mkdir -p /u01/app/oracle/fast_recovery_area/DB11G
$ mkdir -p /u01/app/oracle/admin/DB11G/adump
Copy the files from the primary to the standby server.
$ # Standby controlfile to all locations.
$ scp oracle@ol5-112-dga1:/tmp/db11g_stby.ctl /u01/app/oracle/oradata/DB11G/control01.ctl
$ cp /u01/app/oracle/oradata/DB11G/control01.ctl /u01/app/oracle/fast_recovery_area/DB11G/control02.ctl
$ # Parameter file.
$ scp oracle@ol5-112-dga1:/tmp/initDB11G_stby.ora /tmp/initDB11G_stby.ora
$ # Remote login password file.
$ scp oracle@ol5-112-dga1:$ORACLE_HOME/dbs/orapwDB11G $ORACLE_HOME/dbs
Start Listener
When using active duplicate, the standby server requires static listener configuration in a "listener.ora" file. In this case I used the following configuration.
SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC =
(GLOBAL_DBNAME = DB11G.WORLD)
(ORACLE_HOME = /u01/app/oracle/product/11.2.0/db_1)
(SID_NAME = DB11G)
)
)
LISTENER =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = ol5-112-dga2.localdomain)(PORT = 1521))
)
(DESCRIPTION =
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1521))
)
)
ADR_BASE_LISTENER = /u01/app/oracle
Make sure the listener is started on the standby server.
$ lsnrctl start
Create Standby Redo Logs on Primary Server
The
DUPLICATE command automatically creates the standby redo logs on the standby. To make sure the primary database is configured for switchover, we must create the standby redo logs on the primary server.
ALTER DATABASE ADD STANDBY LOGFILE ('/u01/app/oracle/oradata/DB11G/standby_redo01.log') SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE ('/u01/app/oracle/oradata/DB11G/standby_redo02.log') SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE ('/u01/app/oracle/oradata/DB11G/standby_redo03.log') SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE ('/u01/app/oracle/oradata/DB11G/standby_redo04.log') SIZE 50M;
Create Standby Using DUPLICATE
Start the auxillary instance on the standby server by starting it using the temporary "init.ora" file.
$ export ORACLE_SID=DB11G
$ sqlplus / as sysdba
SQL> STARTUP NOMOUNT PFILE='/tmp/initDB11G_stby.ora';
Connect to RMAN, specifying a full connect string for both the TARGET and AUXILLARY instances. DO not attempt to use OS authentication.
$ rman TARGET sys/password@DB11G AUXILIARY sys/password@DB11G_STBY
Now issue the following DUPLICATE command.
DUPLICATE TARGET DATABASE
FOR STANDBY
FROM ACTIVE DATABASE
DORECOVER
SPFILE
SET db_unique_name='DB11G_STBY' COMMENT 'Is standby'
SET LOG_ARCHIVE_DEST_2='SERVICE=db11g ASYNC VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=DB11G'
SET FAL_SERVER='DB11G' COMMENT 'Is primary'
NOFILENAMECHECK;
A brief explanation of the individual clauses is shown below.
FOR STANDBY: This tells the DUPLICATE command is to be used for a standby, so it will not force a DBID change.FROM ACTIVE DATABASE: The DUPLICATE will be created directly from the source datafile, without an additional backup step.DORECOVER: The DUPLICATE will include the recovery step, bringing the standby up to the current point in time.SPFILE: Allows us to reset values in the spfile when it is copied from the source server.NOFILENAMECHECK: Destination file locations are not checked.
Once the command is complete, we can start the apply process.
Start Apply Process
Start the apply process on standby server.
# Foreground redo apply. Session never returns until cancel.
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE;
# Background redo apply. Control is returned to the session once the apply process is started.
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT FROM SESSION;
If you need to cancel the apply process, issue the following command.
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
If you prefer, you can set a delay between the arrival of the archived redo log and it being applied on the standby server using the following commands.
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DELAY 30 DISCONNECT FROM SESSION;
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE NODELAY DISCONNECT FROM SESSION;
Provided you have configured standby redo logs, you can start real-time apply using the following command.
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE USING CURRENT LOGFILE;
Test Log Transport
On the primary server, check the latest archived redo log and force a log switch.
ALTER SESSION SET nls_date_format='DD-MON-YYYY HH24:MI:SS';
SELECT sequence#, first_time, next_time
FROM v$archived_log
ORDER BY sequence#;
ALTER SYSTEM SWITCH LOGFILE;
Check the new archived redo log has arrived at the standby server and been applied.
ALTER SESSION SET nls_date_format='DD-MON-YYYY HH24:MI:SS';
SELECT sequence#, first_time, next_time, applied
FROM v$archived_log
ORDER BY sequence#;
Protection Mode
There are three protection modes for the primary database:
- Maximum Availability: Transactions on the primary do not commit until redo information has been written to the online redo log and the standby redo logs of at least one standby location. If no standby location is available, it acts in the same manner as maximum performance mode until a standby becomes available again.
- Maximum Performance: Transactions on the primary commit as soon as redo information has been written to the online redo log. Transfer of redo information to the standby server is asynchronous, so it does not impact on performance of the primary.
- Maximum Protection: Transactions on the primary do not commit until redo information has been written to the online redo log and the standby redo logs of at least one standby location. If not suitable standby location is available, the primary database shuts down.
By default, for a newly created standby database, the primary database is in maximum performance mode.
SELECT protection_mode FROM v$database;
PROTECTION_MODE
--------------------
MAXIMUM PERFORMANCE
SQL>
The mode can be switched using the following commands. Note the alterations in the redo transport attributes.
-- Maximum Availability.
ALTER SYSTEM SET LOG_ARCHIVE_DEST_2='SERVICE=db11g_stby AFFIRM SYNC VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=DB11G_STBY';
ALTER DATABASE SET STANDBY DATABASE TO MAXIMIZE AVAILABILITY;
-- Maximum Performance.
ALTER SYSTEM SET LOG_ARCHIVE_DEST_2='SERVICE=db11g_stby NOAFFIRM ASYNC VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=DB11G_STBY';
ALTER DATABASE SET STANDBY DATABASE TO MAXIMIZE PERFORMANCE;
-- Maximum Protection.
ALTER SYSTEM SET LOG_ARCHIVE_DEST_2='SERVICE=db11g_stby AFFIRM SYNC VALID_FOR=(ONLINE_LOGFILES,PRIMARY_ROLE) DB_UNIQUE_NAME=DB11G_STBY';
SHUTDOWN IMMEDIATE;
STARTUP MOUNT;
ALTER DATABASE SET STANDBY DATABASE TO MAXIMIZE PROTECTION;
ALTER DATABASE OPEN;
Database Switchover
A database can be in one of two mutually exclusive modes (primary or standby). These roles can be altered at runtime without loss of data or resetting of redo logs. This process is known as a Switchover and can be performed using the following statements.
-- Convert primary database to standby
CONNECT / AS SYSDBA
ALTER DATABASE COMMIT TO SWITCHOVER TO STANDBY;
-- Shutdown primary database
SHUTDOWN IMMEDIATE;
-- Mount old primary database as standby database
STARTUP NOMOUNT;
ALTER DATABASE MOUNT STANDBY DATABASE;
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT FROM SESSION;
On the original standby database issue the following commands.
-- Convert standby database to primary
CONNECT / AS SYSDBA
ALTER DATABASE COMMIT TO SWITCHOVER TO PRIMARY;
-- Shutdown standby database
SHUTDOWN IMMEDIATE;
-- Open old standby database as primary
STARTUP;
Once this is complete, test the log transport as before. If everything is working fine, switch the primary database back to the original server by doing another switchover. This is known as a switchback.
Failover
If the primary database is not available the standby database can be activated as a primary database using the following statements.
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE FINISH;
ALTER DATABASE ACTIVATE STANDBY DATABASE;
Since the standby database is now the primary database it should be backed up immediately.
The original primary database can now be configured as a standby. If Flashback Database was enabled on the primary database, then this can be done relatively easily (
shown here). If not, the whole setup process must be followed, but this time using the original primary server as the standby.
Flashback Database
It was already mentioned in the previous section, but it is worth drawing your attention to
Flashback Database once more. Although a switchover/switchback is safe for both the primary and standby database, a failover renders the original primary database useless for converting to a standby database. If flashback database is not enabled, the original primary must be scrapped and recreated as a standby database.
An alternative is to enable flashback database on the primary (and the standby if desired) so in the event of a failover, the primary can be flashed back to the time before the failover and quickly converted to a standby database. That process is
shown here.
Read-Only Standby and Active Data Guard
Once a standby database is configured, it can be opened in read-only mode to allow query access. This is often used to offload reporting to the standby server, thereby freeing up resources on the primary server. When open in read-only mode, archive log shipping continues, but managed recovery is stopped, so the standby database becomes increasingly out of date until managed recovery is resumed.
To switch the standby database into read-only mode, do the following.
SHUTDOWN IMMEDIATE;
STARTUP MOUNT;
ALTER DATABASE OPEN READ ONLY;
To resume managed recovery, do the following.
SHUTDOWN IMMEDIATE;
STARTUP MOUNT;
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT FROM SESSION;
In 11g, Oracle introduced the Active Data Guard feature. This allows the standby database to be open in read-only mode, but still apply redo information. This means a standby can be available for querying, yet still be up to date. There are licensing implications for this feature, but the following commands show how active data guard can be enabled.
SHUTDOWN IMMEDIATE;
STARTUP MOUNT;
ALTER DATABASE OPEN READ ONLY;
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT FROM SESSION;
Since managed recovery continues with active data guard, there is no need to switch back to managed recovery from read-only mode in this case.
Snapshot Standby
Introduced in 11g, snapshot standby allows the standby database to be opened in read-write mode. When switched back into standby mode, all changes made whilst in read-write mode are lost. This is achieved using flashback database, but the standby database does not need to have flashback database explicitly enabled to take advantage of this feature, thought it works just the same if it is.
If you are using RAC, turn off all but one of the RAC instances. Make sure the instance is in MOUNT mode.
SHUTDOWN IMMEDIATE;
STARTUP MOUNT;
Make sure managed recovery is disabled.
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE CANCEL;
Convert the standby to a snapshot standby. The following example queries the
V$DATABASE view to show that flashback database is not enabled prior to the conversion operation.
SELECT flashback_on FROM v$database;
FLASHBACK_ON
------------------
NO
ALTER DATABASE CONVERT TO SNAPSHOT STANDBY;
ALTER DATABASE OPEN;
SELECT flashback_on FROM v$database;
FLASHBACK_ON
------------------
RESTORE POINT ONLY
SQL>
You can now do treat the standby like any read-write database.
To convert it back to the physical standby, losing all the changes made since the conversion to snapshot standby, issue the following commands.
SHUTDOWN IMMEDIATE;
STARTUP MOUNT;
ALTER DATABASE CONVERT TO PHYSICAL STANDBY;
SHUTDOWN IMMEDIATE;
STARTUP NOMOUNT;
ALTER DATABASE MOUNT STANDBY DATABASE;
ALTER DATABASE RECOVER MANAGED STANDBY DATABASE DISCONNECT;
SELECT flashback_on FROM v$database;
FLASHBACK_ON
------------------
NO
SQL>
The standby is once again in managed recovery and archivelog shipping is resumed. Notice that flashback database is still not enabled.
For more information see:
