◉ TL;DR
If you already know about Data Guard and want to quickly set up a demo environment using VirtualBox and Vagrant you can follow the instructions in my GitHub repository.
- Oracle Database 19c Data Guard on Oracle Linux 7 (OL7)
- Oracle Database 19c Data Guard on Oracle Linux 8 (OL8)
◉ 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 7.6 and Oracle Database 19c.
◉ The primary server (ol7-19-dg1.locadomain) has a running instance.
◉ The standby server (ol7-19-dg2.locadomain) has a software only installation.
◉ There is nothing blocking communication between the machines over the listener ports. If you are using the default 1521 port, node 1 should be able to communicate to node 2 on 1521 and node 2 should be able communicate with node 1 on 1521. Check network and local firewalls are not blocking the communication.
◉ Primary Server Setup
◉ LoggingCheck 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;
-- Make sure at least one logfile is present.
ALTER SYSTEM SWITCH LOGFILE;
Create standby redo logs on 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 standby redo logs must be created on both servers.
-- If Oracle Managed Files (OMF) is used.
ALTER DATABASE ADD STANDBY LOGFILE THREAD 1 GROUP 10 SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE THREAD 1 GROUP 11 SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE THREAD 1 GROUP 12 SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE THREAD 1 GROUP 13 SIZE 50M;
-- If Oracle Managed Files (OMF) is not used.
ALTER DATABASE ADD STANDBY LOGFILE THREAD 1 GROUP 10 ('/u01/oradata/cdb1/standby_redo01.log') SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE THREAD 1 GROUP 11 ('/u01/oradata/cdb1/standby_redo02.log') SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE THREAD 1 GROUP 12 ('/u01/oradata/cdb1/standby_redo03.log') SIZE 50M;
ALTER DATABASE ADD STANDBY LOGFILE THREAD 1 GROUP 13 ('/u01/oradata/cdb1/standby_redo04.log') SIZE 50M;
If you want to user flashback database, enable it on the primary now, so it will be enabled on the standby also. It's very useful as you will see below.
ALTER DATABASE FLASHBACK ON;
◉ Initialization Parameters
Check the setting for the DB_NAME and DB_UNIQUE_NAME parameters. In this case they are both set to "cdb1" on the primary database.
SQL> show parameter db_name
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_name string cdb1
SQL> show parameter db_unique_name
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_unique_name string cdb1
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. For this example, the standby database will have the value "cdb1_stby".
Make sure the STANDBY_FILE_MANAGEMENT parameter is set.
ALTER SYSTEM SET STANDBY_FILE_MANAGEMENT=AUTO;
◉ 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. Notice the use of the SID, rather than the SERVICE_NAME in the entries. This is important as the broker will need to connect to the databases when they are down, so the services will not be present.
cdb1 =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = ol7-19-dg1)(PORT = 1521))
)
(CONNECT_DATA =
(SID = cdb1)
)
)
cdb1_stby =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = ol7-19-dg2)(PORT = 1521))
)
(CONNECT_DATA =
(SID = cdb1)
)
)
The "$ORACLE_HOME/network/admin/listener.ora" file on the primary server contains the following configuration.
LISTENER =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = ol7-19-dg1)(PORT = 1521))
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1521))
)
)
SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC =
(GLOBAL_DBNAME = cdb1_DGMGRL)
(ORACLE_HOME = /u01/app/oracle/product/19.0.0/db_1)
(SID_NAME = cdb1)
(ENVS="TNS_ADMIN=/u01/app/oracle/product/19.0.0/db_1/network/admin")
)
)
ADR_BASE_LISTENER = /u01/app/oracle
The "$ORACLE_HOME/network/admin/listener.ora" file on the standby server contains the following configuration. Since the broker will need to connect to the database when it's down, we can't rely on auto-registration with the listener, hence the explicit entry for the database.
LISTENER =
(DESCRIPTION_LIST =
(DESCRIPTION =
(ADDRESS = (PROTOCOL = TCP)(HOST = ol7-19-dg2)(PORT = 1521))
(ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1521))
)
)
SID_LIST_LISTENER =
(SID_LIST =
(SID_DESC =
(GLOBAL_DBNAME = cdb1_stby_DGMGRL)
(ORACLE_HOME = /u01/app/oracle/product/19.0.0/db_1)
(SID_NAME = cdb1)
(ENVS="TNS_ADMIN=/u01/app/oracle/product/19.0.0/db_1/network/admin")
)
)
ADR_BASE_LISTENER = /u01/app/oracle
Once the listener.ora changes are in place, restart the listener on both servers.
lsnrctl stop
lsnrctl start
◉ Standby Server Setup
◉ Prepare for DuplicateCreate a parameter file for the standby database called "/tmp/initcdb1_stby.ora" with the following contents.
*.db_name='cdb1'
Create the necessary directories on the standby server.
mkdir -p /u01/app/oracle/oradata/cdb1/pdbseed
mkdir -p /u01/app/oracle/oradata/cdb1/pdb1
mkdir -p /u01/app/oracle/fast_recovery_area/cdb1
mkdir -p /u01/app/oracle/admin/cdb1/adump
Create a password file, with the SYS password matching that of the primary database.
$ orapwd file=/u01/app/oracle/product/19.0.0/db_1/dbs/orapwcdb1 password=Password1 entries=10
◉ Create Standby using DUPLICATE
Start the auxiliary instance on the standby server by starting it using the temporary "init.ora" file.
$ export ORACLE_SID=cdb1
$ sqlplus / as sysdba
SQL> STARTUP NOMOUNT PFILE='/tmp/initcdb1_stby.ora';
Connect to RMAN, specifying a full connect string for both the TARGET and AUXILIARY instances. Do not attempt to use OS authentication.
$ rman TARGET sys/Password1@cdb1 AUXILIARY sys/Password1@cdb1_stby
Now issue the following DUPLICATE command.
DUPLICATE TARGET DATABASE
FOR STANDBY
FROM ACTIVE DATABASE
DORECOVER
SPFILE
SET db_unique_name='cdb1_stby' COMMENT 'Is standby'
NOFILENAMECHECK;
If you need to convert file locations, or alter any initialisation parameters, you can do this during the DUPLICATE using the SET command.
DUPLICATE TARGET DATABASE
FOR STANDBY
FROM ACTIVE DATABASE
DORECOVER
SPFILE
SET db_unique_name='cdb1_stby' COMMENT 'Is standby'
SET db_file_name_convert='/original/directory/path1/','/new/directory/path1/','/original/directory/path2/','/new/directory/path2/'
SET log_file_name_convert='/original/directory/path1/','/new/directory/path1/','/original/directory/path2/','/new/directory/path2/'
SET job_queue_processes='0'
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 datafiles, 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 using the broker.
◉ Enable Broker
At this point we have a primary database and a standby database, so now we need to start using the Data Guard Broker to manage them. Connect to both databases (primary and standby) and issue the following command.
ALTER SYSTEM SET dg_broker_start=true;
On the primary server, issue the following command to register the primary server with the broker.
$ dgmgrl sys/Password1@cdb1
DGMGRL for Linux: Release 19.0.0.0.0 - Production on Tue Feb 26 22:39:33 2018
Version 19.2.0.0.0
Copyright (c) 1982, 2019, Oracle and/or its affiliates. All rights reserved.
Welcome to DGMGRL, type "help" for information.
Connected as SYSDBA.
DGMGRL> CREATE CONFIGURATION my_dg_config AS PRIMARY DATABASE IS cdb1 CONNECT IDENTIFIER IS cdb1;
Configuration "my_dg_config" created with primary database "cdb1"
DGMGRL>
Now add the standby database.
DGMGRL> ADD DATABASE cdb1_stby AS CONNECT IDENTIFIER IS cdb1_stby MAINTAINED AS PHYSICAL;
Database "cdb1_stby" added
DGMGRL>
Now we enable the new configuration.
DGMGRL> ENABLE CONFIGURATION;
Enabled.
DGMGRL>
The following commands show how to check the configuration and status of the databases from the broker.
DGMGRL> SHOW CONFIGURATION;
Configuration - my_dg_config
Protection Mode: MaxPerformance
Members:
cdb1 - Primary database
cdb1_stby - Physical standby database
Fast-Start Failover: DISABLED
Configuration Status:
SUCCESS (status updated 26 seconds ago)
DGMGRL> SHOW DATABASE cdb1;
Database - cdb1
Role: PRIMARY
Intended State: TRANSPORT-ON
Instance(s):
cdb1
Database Status:
SUCCESS
DGMGRL> SHOW DATABASE cdb1_stby;
Database - cdb1_stby
Role: PHYSICAL STANDBY
Intended State: APPLY-ON
Transport Lag: 0 seconds (computed 1 second ago)
Apply Lag: 0 seconds (computed 1 second ago)
Average Apply Rate: 5.00 KByte/s
Real Time Query: OFF
Instance(s):
cdb1
Database Status:
SUCCESS
DGMGRL>
◉ 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 commands. Connect to the primary database (cdb1) and switchover to the standby database (cdb1_stby).
$ dgmgrl sys/Password1@cdb1
DGMGRL for Linux: Release 19.0.0.0.0 - Production on Tue Feb 26 22:39:33 2018
Version 19.2.0.0.0
Copyright (c) 1982, 2019, Oracle and/or its affiliates. All rights reserved.
Welcome to DGMGRL, type "help" for information.
Connected as SYSDBA.
DGMGRL> SWITCHOVER TO cdb1_stby;
Performing switchover NOW, please wait...
Operation requires a connection to instance "cdb1" on database "cdb1_stby"
Connecting to instance "cdb1"...
Connected as SYSDBA.
New primary database "cdb1_stby" is opening...
Operation requires start up of instance "cdb1" on database "cdb1"
Starting instance "cdb1"...
ORACLE instance started.
Database mounted.
Switchover succeeded, new primary is "cdb1_stby"
DGMGRL>
Let's switch back to the original primary. Connect to the new primary (cdb1_stby) and switchover to the new standby database (cdb1).
$ dgmgrl sys/Password1@cdb1_stby
DGMGRL for Linux: Release 19.0.0.0.0 - Production on Tue Feb 26 22:53:36 2018
Version 19.2.0.0.0
Copyright (c) 1982, 2019, Oracle and/or its affiliates. All rights reserved.
Welcome to DGMGRL, type "help" for information.
Connected as SYSDBA.
DGMGRL> SWITCHOVER TO cdb1;
Performing switchover NOW, please wait...
Operation requires a connection to instance "cdb1" on database "cdb1"
Connecting to instance "cdb1"...
Connected as SYSDBA.
New primary database "cdb1" is opening...
Operation requires start up of instance "cdb1" on database "cdb1_stby"
Starting instance "cdb1"...
ORACLE instance started.
Database mounted.
Switchover succeeded, new primary is "cdb1"
DGMGRL>
◉ Database Failover
If the primary database is not available the standby database can be activated as a primary database using the following statements. Connect to the standby database (cdb1_stby) and failover.
$ dgmgrl sys/Password1@cdb1_stby
DGMGRL for Linux: Release 19.0.0.0.0 - Production on Tue Feb 26 22:53:36 2018
Version 19.2.0.0.0
Copyright (c) 1982, 2019, Oracle and/or its affiliates. All rights reserved.
Welcome to DGMGRL, type "help" for information.
Connected as SYSDBA.
DGMGRL> FAILOVER TO cdb1_stby;
Performing failover NOW, please wait...
Failover succeeded, new primary is "cdb1_stby"
DGMGRL>
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 with the following command.
DGMGRL> REINSTATE DATABASE cdb1;
Reinstating database "cdb1", please wait...
Operation requires shut down of instance "cdb1" on database "cdb1"
Shutting down instance "cdb1"...
ORACLE instance shut down.
Operation requires start up of instance "cdb1" on database "cdb1"
Starting instance "cdb1"...
ORACLE instance started.
Database mounted.
Continuing to reinstate database "cdb1" ...
Reinstatement of database "cdb1" succeeded
DGMGRL>
If flashback database is not enabled, you would have to manually recreate cdb1 as a standby. The basic process is the reverse of what you did previously.
# 1) Cleanup the old instance.
sqlplus / as sysdba <<EOF
SHUTDOWN IMMEDIATE;
EXIT;
EOF
rm -Rf /u01/app/oracle/oradata/cdb1/*
rm -Rf /u01/app/oracle/fast_recovery_area/cdb1
rm -Rf /u01/app/oracle/fast_recovery_area/cdb1_stby
rm -Rf /u01/app/oracle/admin/cdb1
mkdir -p /u01/app/oracle/fast_recovery_area/cdb1
mkdir -p /u01/app/oracle/admin/cdb1/adump
mkdir -p /u01/app/oracle/oradata/cdb1/pdbseed
mkdir -p /u01/app/oracle/oradata/cdb1/pdb1
rm $ORACLE_HOME/dbs/spfilecdb1.ora
export ORACLE_SID=cdb1
sqlplus / as sysdba <<EOF
STARTUP NOMOUNT PFILE='/tmp/initcdb1_stby.ora';
EXIT;
EOF
# 2) Connect to RMAN.
$ rman TARGET sys/Password1@cdb1_stby AUXILIARY sys/Password1@cdb1
# 3) Duplicate the database.
DUPLICATE TARGET DATABASE
FOR STANDBY
FROM ACTIVE DATABASE
DORECOVER
SPFILE
SET db_unique_name='cdb1' COMMENT 'Is standby'
NOFILENAMECHECK;
# 4) Connect to DGMDRL on the current primary.
$ dgmgrl sys/Password1@cdb1_stby
# 5) Enable the new standby.
DGMGRL> ENABLE DATABASE cdb1;
◉ 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, as shown above.
◉ 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.
Connect to the primary (cdb1) database and convert the standby database (cdb1_stby) to a snapshot standby.
$ dgmgrl sys/Password1@cdb1
DGMGRL for Linux: Release 19.0.0.0.0 - Production on Tue Feb 26 22:53:36 2018
Version 19.2.0.0.0
Copyright (c) 1982, 2019, Oracle and/or its affiliates. All rights reserved.
Welcome to DGMGRL, type "help" for information.
Connected as SYSDBA.
DGMGRL> CONVERT DATABASE cdb1_stby TO SNAPSHOT STANDBY;
Converting database "cdb1_stby" to a Snapshot Standby database, please wait...
Database "cdb1_stby" converted successfully
DGMGRL>
When you are finished with the snapshot standby, convert it back to a standby database.
$ dgmgrl sys/Password1@cdb1
DGMGRL for Linux: Release 19.0.0.0.0 - Production on Tue Feb 26 22:53:36 2018
Version 19.2.0.0.0
Copyright (c) 1982, 2019, Oracle and/or its affiliates. All rights reserved.
Welcome to DGMGRL, type "help" for information.
Connected as SYSDBA.
DGMGRL> CONVERT DATABASE cdb1_stby TO PHYSICAL STANDBY;
Converting database "cdb1_stby" to a Physical Standby database, please wait...
Operation requires shut down of instance "cdb1" on database "cdb1_stby"
Shutting down instance "cdb1"...
Database closed.
Database dismounted.
ORACLE instance shut down.
Operation requires start up of instance "cdb1" on database "cdb1_stby"
Starting instance "cdb1"...
ORACLE instance started.
Database mounted.
Continuing to convert database "cdb1_stby" ...
Database "cdb1_stby" converted successfully
DGMGRL>
The standby is once again in managed recovery and archivelog shipping is resumed. Notice that flashback database is still not enabled.
DGMGRL> SHOW CONFIGURATION;
Configuration - my_dg_config
Protection Mode: MaxPerformance
Members:
cdb1 - Primary database
cdb1_stby - Physical standby database
Fast-Start Failover: DISABLED
Configuration Status:
SUCCESS (status updated 38 seconds ago)
DGMGRL>
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