Redo and archive log setup

You can access both online and archive logs by default. If you want to access only the online logs, Mirror Replication Agent can be configured to do so, but it requires that you turn auto-archiving off and requires Mirror Replication Agent to issue manual archive log commands to Oracle.

When the default is used and archive log files are to be accessed, Mirror Replication Agent must be configured to use a directory path where archive log files are located. By default, an Oracle instance creates multiple directories under the flash recovery area specified by the DB_RECOVERY_FILE_DEST parameter of the Oracle ALTER SYSTEM command, each directory corresponding to and named after a separate day. However, Mirror Replication Agent requires mirrored archived redo log files to reside in a single directory. Consequently, you must configure Oracle to archive to a single directory to be read by Mirror Replication Agent.

For information on specifying archive log destinations for your Oracle environment, see the Oracle ALTER SYSTEM command and LOG_ARCHIVE_DEST_n parameter.

Because archive log files are always files, not raw devices, you must be careful to ensure the disk replication system and file system at the remote site allows the archive logs to be accessed from the remote site. If the disk replication system or remote file system does not provide a means to have access to archived log files from the primary site, the archive log files must be provided to the remote site outside of disk replication.As an example, if the file system on the remote site does not recognize files replicated using disk replication, you can write a copy of the archive log files directly from the primary to a remote system's device, using a remote mount. To do this, make a remote site device mountable to the primary system and mount that device at the primary site. Then, configure Oracle to write an additional copy of the archive log files to this remote device. See the Oracle ALTER SYSTEM command and LOG_ARCHIVE_DEST_n parameter for details on adding additional archive log destinations to your Oracle environment.

In the Mirror Replication Agent, set configuration property pdb_archive_path to the remote device location. You can also set Mirror Replication Agent configuration parameter pdb_remove_archives to true, to allow the Replication Agent to remove these archive log files when they are no longer needed to support replication.

When pdb_include_archives is set to true (the default) Mirror Replication Agent does not archive, and Sybase recommends that you configure Oracle to do automatic archiving of redo logs.

When the configuration parameter pdb_include_archives is set to false, Mirror Replication Agent for Oracle requires that automatic archiving of Oracle redo logs be disabled. Archiving is performed manually by Mirror Replication Agent as the data in the mirrored redo log files is replicated.

Mirror Replication Agent for Oracle requires the following settings in your Oracle database depending on the Oracle version.

1. Make sure you have SYSDBA administrator privileges, and close the database.

2. Enter the following:

   alter database ARCHIVELOG MANUAL;
   

3. Verify that log archiving is disabled:

   select log_mode from v$database;
   

   If MANUAL is returned, then automatic log archiving is disabled.

1. To change the log_archive_start parameter, you can manually edit the server’s start-up parameter file or use the following Oracle command:

   alter system set log_archive_start=false scope=spfile;
   

2. Check the setting of the log_archive_start parameter:

   select value from v$system_parameter where name = 'log_archive_start';
   

3. If false is returned, the value in the server parameter file has been correctly modified to prevent automatic archiving when you restart the Oracle server. For more information about the log_archive_start parameter or the alter system command, see the Oracle Database Reference Manual.

4. Automatic archiving must be disabled in the active server and when you restart the Oracle server. To stop automatic archiving in the active server:

   alter system archive log stop;
   

5. To disable automatic archiving when you restart the Oracle server, change the value of the server’s log_archive_start parameter to false.

   This note applies only when pdb_include _archives is set to false. For redo log file processing after Mirror Replication Agent for Oracle is initialized, automatic archiving must never be enabled, even temporarily. If automatic archiving is re-enabled or manual archiving is performed, causing a redo log file not yet processed by Mirror Replication Agent to be overwritten, then the data in the lost redo log file will not be replicated. You can recover from this situation by reconfiguring Mirror Replication Agent to access archive log files. Set pdb_include_archives to true, set pdb_archive_path to the directory location that contains the archive of the file that has been overwritten, and resume. After catching up, suspend Mirror Replication Agent, and reset pdb_include_archives to false.

You can enable the forced logging of all database changes to the Oracle redo log file. Sybase recommends setting this option to insure that all data that should be replicated is logged. To enable the force logging command, execute the following statement on the primary database:

alter database FORCE LOGGING;

To verify the current setting of the force logging command, execute the following statement on the primary database:

select force_logging from v$database;