Truncating the transaction log

Mirror Replication Agent provides features for both automatic and manual log truncation.

Mirror Replication Agent provides two options for automatic transaction log truncation:

• Periodic truncation, based on a time interval you specify

• Automatic truncation whenever Mirror Replication Agent receives a new LTM Locator value from the primary Replication Server

You also have the option to switch off automatic log truncation. By default, automatic log truncation is switched off.

To specify the automatic truncation option you want (including none), use the ra_config command to set the value of the truncation_type configuration parameter.

To truncate the transaction log automatically based on a time interval, use the ra_config command to set the value of the truncation_interval configuration parameter.

At any time, you can truncate the Mirror Replication Agent transaction log manually by invoking the pdb_truncate_xlog command at the Mirror Replication Agent administration port.

To truncate the transaction log at a specific time, use a scheduler utility to execute the pdb_truncate_xlog command automatically.

Mirror Replication Agent for Microsoft SQL Server truncates the primary database log in units of transactions. After Mirror Replication Agent for Microsoft SQL Server receives the LTM locator from Replication Server, Mirror Replication Agent for Microsoft SQL Server queries the primary database to obtian the transaction ID of the newest transaction that can be truncated. Mirror Replication Agent for Microsoft SQL Server then marks as reusable the transaction log space before the newest transaction. Microsoft SQL Server can then write log records into the reusable space.

The sp_repltrans and sp_repldone Microsoft SQL Server commands are issued by Mirror Replication Agent to control log truncation within Microsoft SQL Server. These commands require that the Mirror Replication Agent user have the db_owner role permission.