This type of database does not have any datafiles, all it does is receive archived logs from primary, and retransmit. Nor does it perform any media recovery, but it can compress the logs during re-transmission. It is transparent to the dba during switchover/failover operations.
This type of database is useful when primary and standby are too far apart to allow redo transport in synchronous mode. The recommended set up is synchronous redo transport between primary and its far sync standby, and asynchronous transport to the actual failover/swictchover target.
This arrangement allows zero data loss configuration across large distances because there is efficient synchronous redo transport from primary to far sync standby.
Far sync standby also relieves primary from the overhead of transmitting redo to multiple sites.
Always, the far sync instance is located close enough to the primary redo source to allow synchronous redo transport.
For the scenario where the physical and terminal standby have exchanged their roles, its necessary to have a far sync standby close to the new primary, to receive its redo synchronously, and to transmit the redo to the new standby.
Below is a discussion on the creation of a far sync standby database.
Scenario:
There is a CDB called CDB2 in a Data Guard Max Performance configuration using a physical standby. The primary and terminal standby are already in a data guard configuration using the Max Performance protection.
A Far sync db site will be inserted into the configuration, and the configuration will be upgraded to Max Availability.
Query issued at Primary showing initial configuration
-----------------------------------------------------------------
SQL> select * from v$dataguard_config;
DB_UNIQUE_NAME PARENT_DBUN DEST_ROLE CURRENT_SCN CON_ID
---------------- ------------- ----------------- ----------- ------
SCOTT NONE PRIMARY DATABASE 888526 0
TIGER SCOTT PHYSICAL STANDBY 888529 0
SQL> select protection_level from v$database;
PROTECTION_LEVEL
--------------------
MAXIMUM PERFORMANCE
A far sync stanbdy (FSS) will be added to the configuration, to be in sync redo transport with the primary SCOTT. It will forward the recieved redo asynchronously to the terminal standby identified by TIGER.
There will be eventually 3 sites in the configuration
1. A Primary database - identified by the unique name SCOTT
2. A Far Sync standby - identified by the unique name FSS
3. A terminal standby - identified by the unique name TIGER
Steps to add a Data Guard Far Sync standby instance
1. On all 3 sites, create a tnsnames entry for the new far sync standby instance, called CDB2_FSS.
Already tnsnames entry would exist for the original primary (CDB2_SCOTT) and original standby (CDB2_TIGER) from the previous data guard set up.
CDB2_FSS =
(DESCRIPTION =
(ADDRESS_LIST =
(ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.1.107)(PORT = 1521))
)
(CONNECT_DATA =
(SERVICE_NAME = FSS)
)
)
2. On the far sync host, create a static listener registration entry for the far-sync standby instance
In the netmgr gui, go to the listener database services configuraiton, and click Add database service.
Supply these values in the textboxes as indicated
For example, the listener.ora static registration entry could be:
Global Database Name : FSS
Oracle Home : /u01/app/oracle/product/12.1.0/dbhome_1
SID : CDB2
On the far sync host again, re-load the listener and check the static registration of the service FSS
-----------------------------------------------------------------------------------------------------
[oracle@laboms oradata]$ lsnrctl reload
LSNRCTL for Linux: Version 12.1.0.1.0 - Production on 05-FEB-2014 18:27:23
Copyright (c) 1991, 2013, Oracle. All rights reserved.
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=laboms.example.com)(PORT=1521)))
The command completed successfully
[oracle@laboms oradata]$ lsnrctl services
LSNRCTL for Linux: Version 12.1.0.1.0 - Production on 05-FEB-2014 18:48:20
Copyright (c) 1991, 2013, Oracle. All rights reserved.
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=laboms.example.com)(PORT=1521)))
Services Summary...
Service "FSS" has 1 instance(s).
Instance "CDB2", status UNKNOWN, has 1 handler(s) for this service...
Handler(s):
"DEDICATED" established:0 refused:0
LOCAL SERVER
...
...
3. Copy the primary site's Oracle password file from primary site to the far sync site using ftp
This can be done using scp/ftp4. Check that you are able to connect to it using tnsnames
[oracle@laboms ~]$ sqlplus sys/oracle@cdb2_ffs as sysdba
SQL*Plus: Release 12.1.0.1.0 Production on Tue Feb 4 14:35:04 2014
Copyright (c) 1982, 2013, Oracle. All rights reserved.
Connected to an idle instance.
5. Modify primary Data Guard parameters for sending archive logs to the far sync instance
log_archive_config:Purpose: This is the list of db_unique_names of sites partitipating in the configuration.
Set this to DG_CONFIG=(scott,fss,tiger)'
log_archive_dest_1:
Purpose : Use fast recovery area for local archiving. Set the db_unique_name attribute to CDB2_SCOTT for the far sync instance.
Set this to 'location=use_db_recovery_file_dest db_unique_name=CDB2_SCOTT';
log_archive_dest_2:
Purpose : Send archive logs to the far sync instance synchronously.
Set this to 'service=CDB2_FSS SYNC valid_for(online_logfiles,primary_role) db_unique_name=FSS'
6. Create a far-sync standby controlfile using the primary
SQL>alter database create far sync instance controlfile as 'fss_control1.ctl';Database altered.
Next, copy the controlfile to the far sync site.
7. Copy the primary spfile as a pfile to far sync site and modify the following parameters.
SQL> create pfile='/home/oracle/fss_pfile.ora' from spfile;File created.
Next, copy the modified pfile to the far sync standby site, and modify these parameters.
db_unique_name:
Purpose: uniquely identifies the far sync site.
Set this to 'fss'
log_archive_config:
Purpose: List of sites partitipating in redo transport
Set this to 'DG_CONFIG=(SCOTT,FSS,TIGER)'
log_archive_dest_1:
Purpose : Set local archiving destination. Far syns instance will locally archive the received files first.
Set this to 'location=use_db_recovery_file_dest db_unique_name=FSS'
log_archive_dest_2:
Purpose: Set remote archiving destination. The far sync site archives asynchronously to terminal standby.
Set this to 'service=CDB2_TIGER ASYNC valid_for=(standby_logfiles,standby_role) db_unique_name=TIGER'
control_files:
Purpose: Set location of the far sync instance controlfiles
Set this to '/u01/app/oracle/oradata/cdb2_fss/fss_control1.ctl'
log_file_name_convert:
Purpose: Set primary-->far sync file path translation for sync standby redo log files.
Set this to '/u01/app/oracle/oradata/cdb2','/u01/app/oracle/oradata/cdb2_fss'
fal_server:
Purpose: Set the site for archive log gap resolution
Set this to 'SCOTT'
8. Startup the far sync standby intance using the pfile
We are using the net service name cdb2_fss created previously to connect to this instance and start it up.[oracle@fss cdb2_fss]$ sqlplus sys/oracle@cdb2_fss as sysdba
SQL*Plus: Release 12.1.0.1.0 Production on Fri Feb 7 12:32:56 2014
Copyright (c) 1982, 2013, Oracle. All rights reserved.
Connected to an idle instance.
SQL> startup nomount pfile='fss_pfile.ora';
ORACLE instance started.
Total System Global Area 1570009088 bytes
Fixed Size 2288776 bytes
Variable Size 1241514872 bytes
Database Buffers 318767104 bytes
Redo Buffers 7438336 bytes
SQL>
9. Mount the database and check the standby logs
SQL> alter database mount;Database altered.
SQL> select a.group#,substr(b.member,1,45) member,b.type,a.sequence#
from v$standby_log a join v$logfile b on (a.group#=b.group#);
GROUP# MEMBER TYPE SEQUENCE#
---------- --------------------------------------------- ------- ----------
3 /u01/app/oracle/oradata/cdb2_fss/root/sby1.or STANDBY 0
4 /u01/app/oracle/oradata/cdb2_fss/root/sby4.or STANDBY 0
5 /u01/app/oracle/oradata/cdb2_fss/root/sby5.or STANDBY 0
So far, no logs have been received at the ffs site from primary.
Remember to create an spfile for the far sync instance using CREATE SPFILE from memory.
10. Check the archive destination status at the primary to see if its able to send archived logs to the far sync site.
Initially it showed an error;SQL> select dest_id, status, error, archived_seq# from v$archive_dest_status where dest_id in (1,2);
DEST_ID STATUS ERROR ARCHIVED_SEQ#
---------- --------- -------------------------------------------------------
1 VALID 69
2 ERROR ORA-01094: ALTER DATABASE or ALTER PLUGGABLE DATA 0
BASE CLOSE inprogress. Connections not permitted
But soon it resolved by itself.
SQL> select dest_id, status,error, archived_seq# from
2 v$archive_dest_status where dest_id in (1,2);
DEST_ID STATUS ERROR ARCHIVED_SEQ#
---------- --------- ----- -------------
1 VALID 75
2 VALID 75
11. Force a log file switch on primary to test archive log transport
SQL> alter system switch logfile;System altered.
SQL> archive log list;
Database log mode Archive Mode
Automatic archival Enabled
Archive destination USE_DB_RECOVERY_FILE_DEST
Oldest online log sequence 76
Next log sequence to archive 77
Current log sequence 77
12. Query the archive destination status on the primary, to see if the logs were archived successfully to the far sync instance
SQL> select dest_id, status, error, archived_seq# from v$archive_dest_status where dest_id in (1,2);DEST_ID STATUS ERROR ARCHIVED_SEQ#
---------- ---------- -------- -------------
1 VALID 76
2 VALID 76
Examine the current protection level of the configuration
---------------------------------------------------------
SQL> select protection_level from v$database;
PROTECTION_LEVEL
--------------------
MAXIMUM PERFORMANCE
13. Upgrade the protection mode of the data guard configuration to max availability
SQL> alter database set standby to maximize availability;
Database altered.
14. Check the v$dataguard_config view to examine the data guard configuration
Below the data guard configuration status is queried, after a few more log file switches were done on primary for testing.SQL> select * from v$dataguard_config;
DB_UNIQUE_NAME PARENT_DBUN DEST_ROLE CURRENT_SCN CON_ID
------------------------ ------------ ----------------- ----------- ------
SCOTT NONE PRIMARY DATABASE 944193 0
FSS SCOTT FAR SYNC INSTANCE 944104 0
TIGER FSS PHYSICAL STANDBY 944104 0
