Chapter 4: Replication Agent for Oracle

Redo log setup

The Replication Agent for Oracle must be installed on a machine where it can directly access the Oracle redo logs.

Replication Agent for Oracle requires that automatic archiving of Oracle redo logs be disabled. Archiving is performed manually by the Replication Agent as the data in the redo logs ia replicated. The following tasks should not be performed until the Replication Agent is ready to be initialized, so that archiving of redo logs will continue to take place.

Replication Agent for Oracle requires the following settings in your Oracle database:

Redo log archiving must be enabled. To enable redo log archiving, execute the following command:
```
alter database ARCHIVELOG;
```
To verify that log archiving is enabled, execute the following query:
```
select log_mode from v$database;
```
If ARCHIVELOG is returned, then log archiving is enabled.
Automatic archiving must be disabled in the active server and when you re-start the Oracle server. To stop automatic archiving in the active server, enter the following Oracle command:
```
alter system archive log stop;
```
To disable automatic archiving when you re-start the Oracle server, change the value of the server’s LOG_ARCHIVE_START parameter to FALSE.

You can change the LOG_ARCHIVE_START parameter by manually editing the server’s startup parameter file, or with the following Oracle command:
```
alter system set log_archive_start=false scope=spfile;
```
To check the setting of the LOG_ARCHIVE_START parameter, execute the following query:
```
select value from v$system_parameter where name = 'log_archive_start';
```
If FALSE is returned, then the value in the server parameter file has been correctly modified to prevent automatic archiving when you re-start the Oracle server.

For more information about the LOG_ARCHIVE_START parameter, or the ALTER SYSTEM commands, see the Oracle database reference guide.

After 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 the Replication Agent to be overwritten, then the data in the lost redo log file will not be replicated. To recover from this situation requires that the replicate be rematerialized.
In Oracle release 9.2 and later, supplemental logging of primary key data and index columns must be enabled. To enable supplemental logging, execute the following Oracle command:
```
alter database add SUPPLEMENTAL LOG DATA (PRIMARY KEY, UNIQUE INDEX) COLUMNS;
```
To verify that supplemental logging of primary key information is enabled, execute the following query:
```
select SUPPLEMENTAL_LOG_DATA_PK from v$database;
```
If YES is returned, then supplemental logging of primary key information is enabled.

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;

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