Availability and Recovery - The valid_for Attribute
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The valid_for attribute is a new attribute that can be associated with the log_ archive_dest_n parameter in Oracle Database 10g. This attribute allows you to define when an archive log destination will be used and the role of the archived redo at that destination.
The valid_for attribute takes two parameters, the archival_source parameter and the database_role parameter. The archival_source parameter defines when the destination is used. Valid settings for this parameter are as follows:
- ONLINE_LOGFILE This destination is used only when archiving online redo log files. This destination is not used when archiving standby redo log files, or if log files are being received from another database.
- STANDBY_LOGFILE This destination is used only when standby redo log files are being archived or if archived redo logs are being received from another database.
- ALL_LOGFILES This destination can be used in either role, archiving online or standby redo log files.
The database_role parameter is the second parameter of the valid_for attribute. As the name implies, this parameter defines the role of the database that the parameter is associated with and, thus, when the archive log destination will be used. Valid settings for this parameter are as follows:
- PRIMARY_ROLE This destination is used only when the database is in the primary database role.
- STANDBY_ROLE This destination is used only when the database is in a standby role. This applies to both physical and logical standby databases.
- ALL_ROLES Open the barn doors Bessie! This destination is used if the database is in primary or standby mode.
The parameters for the valid_for attribute can be specified in any order, but only specific combinations are valid for the attribute. For example, the combination of STANDBY_LOGFILE and PRIMARY_ROLE is invalid and will generate an error at database startup.
Here is an example of an archivelog destination having been set, using the valid_for attribute of the log_archive_dest_1 parameter:
LOG_ARCHIVE_DEST_1= service=STANDBY_DB VALID_FOR = (STANDBY_LOGFILE, STANDBY_ROLE)
Data Dictionary Views and valid_for
The V$ARCHIVE_DEST data dictionary view has a new column, VALID_NOW, that indicates if the archivelog destination will be used. Valid values include
- YES The destination is properly defined and will be used.
- WRONG VALID_TYPE The archivelog destination is properly defined, but in the current role it cannot be used. This might occur if the archive log destination was defined for a standby database, and the database was currently configured as a primary database.
- WRONG VALID_ROLE The archivelog destination is not defined correctly for the current database role (primary or standby).
- UNKNOWN Indicates that the archivelog destination is not defined.
Also, the V$ARCHIVE_DEST view provides two additional new columns, VALID_TYPE and VALID_ROLE, that allow you to see how the valid_for parameter for each archivelog destination is configured.
Redo Transmission Enhancements
Oracle Database 10g provides two new enhancements with regard to redo transmission. First of all, database authentication must now be set up for all databases. This means that the remote_login_passwordfile parameter must be set to either SHARED or EXCLUSIVE at both the primary and all standby sites. Also, a password file must be generated, and all SYS passwords must be set the same at all sites. If you change the SYS password, it will be automatically changed at all sites.
Oracle Database 10g now also supports encryption of the redo stream to the standby databases as an optional feature. You must have the Oracle Advanced Security option installed at all database sites, and have configured Oracle Net for encryption and integrity checksumming.
 This chapter is from Oracle Database 10g New Features, by Robert Freeman (McGraw-Hill/Osborne, 2004, ISBN: 0072229470). Check it out at your favorite bookstore today. Buy this book now.
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