The Replication Agent uses the value of the LTM locator received from the primary Replication Server to determine where it should begin looking in the UDB transaction log for transactions to be sent to the Replication Server.
The Replication Agent for UDB uses the LTM locator value as follows:
When the value of the LTM locator received from Replication Server and the LTM locator stored by Replication Agent are both zero (0), the Replication Agent positions the Log Reader component at the end of the UDB transaction log.
WARNING! In the event that both LTM locator values are zero, two specific conditions could cause data loss:
When the Replication Agent Log Reader component goes to the Replicating state, it does so asynchronously. When you receive a prompt after invoking the resume command, the Log Reader component may not be finished getting into the Replicating state and positioning itself at the end of the log. If you mark a table immediately after the prompt returns from the resume command, the record containing the mark information could be written to the log before the Log Reader component has positioned itself. In that case, the Log Reader component will miss that record and not replicate any subsequent data for that table. To avoid this problem, wait a short time after invoking the resume command before you mark a table for replication.
If you mark a table for replication, insert data into the table, and then resume replication, the data will not be replicated if the LTM Locators for Replication Agent and Replication Server are zero (as they would be at the beginning of replication). This problem occurs because when both LTM Locators are zero, resuming replication repositions the Log Reader component at the end of the log, skipping over any previous transactions. To avoid this problem when the LTM Locators for Replication Agent and Replication Server are zero, mark the table for replication after you have issued the resume command.
When both the value of the LTM locator received from Replication Server and the LTM locator stored by Replication Agent are not zero, Replication Agent uses the LTM locator value it received from Replication Server to determine the starting position of the oldest open transaction and positions the Log Reader component at that location in the UDB transaction log.
When the value of the LTM locator received from Replication Server is zero (0) and the value of the LTM locator stored by Replication Agent is not zero, Replication Agent uses the LTM locator value it has stored to determine the starting position of the oldest open transaction and positions the Log Reader component at that location in the UDB transaction log.
