log_archive_dest valid_for Tips Oracle Database Tips by Donald BurlesonDecember 19, 2015

Oracle Data Guard - VALID_FOR Attribute

One method of approaching this challenge was by using the symmetrical initialization parameter file as explained in Chapter 3, "Implementing Standby Databases". Some DBAs keep two versions of the initialization parameter file to cater different database roles. Oracle10g has removed the need to alter the log management related initialization parameters during role transition by introducing a new attribute of the log_archive_dest_n parameter called VALID_FOR. This attribute is defined using two arguments redo_log_type and database_role as shown below:

LOG_ARCHIVE_DEST_n='SERVICE=service_name VALID_FOR=(redo_log_type,database_role)'

These two arguments identify the role of the database specified by the log_archive_dest_n parameter and the type of redo log file used at that destination.

• The valid values of redo_log_type are ONLINE_LOGFILE, STANDBY_LOGFILE and ALL_LOGFILES.

• The second argument, database_role, can take the value of the PRIMARY_ROLE, the STANDBY_ROLE or ALL_ROLES.

VALID_FOR Attribute

Combining these two arguments give nine possible values for the attribute VALID_FOR. However, the combination (STANDBY_LOGFILE, PRIMARY_ROLES) is not acceptable, because there cannot be active standby redo log files on the primary database. The default combination is (ALL_LOGFILES, ALL_ROLES). The following snippet from the init.ora file shows an example of the VALID_FOR attribute:

LOG_ARCHIVE_DEST_1='LOCATION=/oracle/appsdb/arch VALID_FOR=(ONLINE_LOGFILE, ALL_ROLE)'
LOG_ARCHIVE_DEST_2='SERVICE=phystdydb VALID_FOR=(ONLINE_LOGFILE,
PRIMARY_ROLE)'
LOG_ARCHIVE_DEST_3='SERVICE=logstdbydb VALID_FOR=(ONLINE_LOGFILE,
PRIMARY_ROLE)'
LOG_ARCHIVE_DEST_4='LOCATION=/oracle/appsdb/archSRL VALID_FOR
(STANDBY_LOGFILE,STANDBY_ROLE)'

In the example given above, log_archive_dest_1 is valid only for the primary database role and the logical Oracle instance role.

On the logical standby site, the redo data generated from the logical Oracle instance will be archived in this location. It will not contain the archived standby redo log files.

On the physical standby site, this destination will not play any part because the RFS process decides the archival destination based on the standby_archive_dest parameter, and the MRP uses the archived log files from this location. log_archive_dest_2 and log_archive_dest_3 are only valid when the database is operating in the primary role.

VALID_FOR Attribute

A proper Oracle Net configuration as detailed in Chapter 3, "Implementing Standby Databases", is the key to the seamless use of the VALID_FOR attribute during role transition. log_archive_dest_4 is only valid if the standby databases have standby redo log files configured.

            Do not use (ALL_LOGFILES, ALL_ROLES) for log archival destination that is a logical standby database. This may overwrite the online log files local to the logical standby database.