Using Standby as an Alternate for Far Sync (12c): Limitations and Considerations

Based on Oracle 12.1

The Recommended Data Guard configuration is in Maximum Availability mode, when using Far Sync which is located near the Primary:

Primary Database à Far Sync Instance - Network input/output (I/O) is synchronous (Sync).

Far Sync Instance à Standby Database – Network I/O is asynchronous (Async).

Primary Database à Standby Database  – As an alternate (when Far Sync is not reachable), network I/O is asynchronous (Async).

Using SQL

If you do not use Data Guard Broker (dgmgrl), use the parameters specified below.

·        Primary

On the Primary Database

Mandatory Parameters

Parameter	Value	Remarks
LOG_ARCHIVE_DEST_2		point to Far Sync service
Alternate	log_archive_dest_3	Switches to the standby destination, after the number of failures specified in the next parameter is reached.
max_failure	1	This value must be higher than 0 (infinite number of retries), but should not be too high, because the connection must fail after n attempts and fail over to the next destination, specified in the alternate parameter.
SYNC
LOG_ARCHIVE_DEST_STATE_2	enable
LOG_ARCHIVE_DEST_3		point to Standby service
Alternate	log_archive_dest_2	Establishes connection with the Far Sync host after the connection with log_dest_3 (standby) failed. Once Standby is up and available again, connection with the standby host is re-established.
max_failure	0	Establishes connection infinitely; never stops retrying.
ASYNC
LOG_ARCHIVE_DEST_STATE_3	alternate

Example:

ALTER SYSTEM SET log_archive_dest_2='service="[FARSYNC_INST]", SYNC  max_failure=1 db_unique_name="[FARSYNC_INST]" alternate=LOG_ARCHIVE_DEST_3 valid_for=(online_logfile,all_roles)';

ALTER SYSTEM SET log_archive_dest_state_2=enable;

ALTER SYSTEM SET log_archive_dest_3='service="[STANDBY_INST]", SYNC max_failure=0 db_unique_name="[STANDBY_INST]" alternate=LOG_ARCHIVE_DEST_2 valid_for=(online_logfile,all_roles)';

ALTER SYSTEM SET log_archive_dest_state_2=alternate;

·        On the Far Sync Instance

Mandatory parameters

Parameter	Value	Remarks
LOG_ARCHIVE_DEST_2		point to Standby service
max_failure	0	This value must be higher than 0 (infinite number of retries), but should not be too high, because the connection must fail after n attempts and fail over to the next destination, specified in the alternate parameter.
ASYNC
NOAFFIRM
LOG_ARCHIVE_DEST_STATE_2	enable

Example:

ALTER SYSTEM SET log_archive_dest_2='service="[STANDBY_INST]", ASYNC max_failure=0 db_unique_name="[STANDBY_INST]" valid_for=(standby_logfile,all_roles)';

ALTER SYSTEM SET log_archive_dest_state_2=enable;

ALTER SYSTEM SET log_archive_dest_3='service="[STANDBY_INST]", SYNC max_failure=0 db_unique_name="[STANDBY_INST]" net_timeout=30 alternate=LOG_ARCHIVE_DEST_2 valid_for=(online_logfile,all_roles)';

ALTER SYSTEM SET log_archive_dest_state_2=alternate;

·        On Standby Database

Mandatory parameters

Parameter	Value	Remarks
LOG_ARCHIVE_DEST_2		Point to Far Sync service only if you have local/near Far Sync. Otherwise, points to the original primary service. Note: Set this parameter only when using switchover.
Alternate	log_archive_dest_3	Switches to original primary destination after the number of failures specified in the next parameter is reached. Note: Set this only when using switchover and only if Far Sync is used as the service destination.
max_failure	1	This value must be higher than 0 (infinite number of retries), but should not be too high, because the connection must fail after n attempts and fail over to the next destination, specified in the alternate parameter.
SYNC
LOG_ARCHIVE_DEST_STATE_2	enable	Set this only when using switchover.
LOG_ARCHIVE_DEST_3		Points to the original Primary service. Note: Set this parameter only when using switchover and if Far Sync is used as service destination.
Alternate	log_archive_dest_2	Establishes connection with the Far Sync destination after the connection with the Primary service failed. Once the Primary service is up and available again, connection with the Primary host is re-established. Note: Set this parameter only when using switchover and if Far Sync is used as service destination.
max_failure	0	Establishes connection infinitely; never stops retrying.
ASYNC
LOG_ARCHIVE_DEST_STATE_3	alternate	Set this parameter only when using switchover.

Example:

ALTER SYSTEM SET log_archive_dest_2='service="[FARSYNC_INST]", SYNC max_failure=1 db_unique_name="[FARSYNC_INST]" alternate=LOG_ARCHIVE_DEST_3 valid_for=(online_logfile,all_roles)';

ALTER SYSTEM SET log_archive_dest_state_2=enable;

ALTER SYSTEM SET log_archive_dest_3='service="[PRIMARY_INST]", SYNC max_failure=0 db_unique_name="[PRIMARY_INST]" alternate=LOG_ARCHIVE_DEST_2 valid_for=(online_logfile,all_roles)';

ALTER SYSTEM SET log_archive_dest_state_2=alternate;

Using Broker

Must have parameters

Parameter	Value	Remark	Target Type
MaxFailure	0		Primary + Standby
MaxFailure	1		Far Sync
RedoRoutes	'([PRIMARY_INST] : [STANDBY_INST] ASYNC)([STANDBY_INST] : [PRIMARY_INST] ASYNC)'		Far Sync
RedoRoutes	'(LOCAL : [FARSYNC_INST] SYNC ALT =( [PRIMARY_INST] ASYNC FALLBACK))'		Standby
RedoRoutes	'(LOCAL : [FARSYNC_INST] SYNC ALT =( [STANDBY_INST] ASYNC FALLBACK))'		Primary

Example:

EDIT FAR_SYNC [FARSYNC_INST] SET PROPERTY RedoRoutes = '([PRIMARY_INST] : [STANDBY_INST] ASYNC)([STANDBY_INST] : [PRIMARY_INST] ASYNC)';

EDIT DATABASE [PRIMARY_INST] SET PROPERTY MaxFailure = 0;

EDIT FAR_SYNC [FARSYNC_INST] SET PROPERTY MaxFailure = 1;

EDIT DATABASE [STANDBY_INST] SET PROPERTY MaxFailure = 0;

EDIT DATABASE [STANDBY_INST] SET PROPERTY RedoRoutes = '(LOCAL : [FARSYNC_INST] SYNC ALT =( [PRIMARY_INST] ASYNC FALLBACK))';   

EDIT DATABASE [PRIMARY_INST] SET PROPERTY RedoRoutes = '(LOCAL : [FARSYNC_INST] SYNC ALT =( [STANDBY_INST] ASYNC FALLBACK))';

EDIT CONFIGURATION SET PROTECTION MODE AS MAXAVAILABILITY;