If multiple Data Mover servers are installed in your environment, you can use the Data Mover synchronization service to create a backup system that can be used as a temporary active system in case of daemon failure on the original active system.
- Active server
- Refers to the Data Mover server on which the daemon is running.
- Standby server
- Refers to one or more Data Mover servers on which the daemon is not running. Standby servers can be used as a primary system in case of failure on the active server.
Replication begins for the first time when the synchronization service running on the server that is used for the standby repository connects through a TCP/IP socket to the system that is used for the active repository. When the synchronization service starts, updates to the active repository are replicated automatically on the standby repository.
As part of the failover functionality, when the standby server is unavailable (offline, down, restarting), the active repository continues to log updates. When a connection is re-established with the standby server, all interim updates from the active repository that occurred when the standby server was unavailable are applied to the standby repository.
If the standby is down too long, interim updates accumulate and may cause a memory issue on the active synchronization service. When a standby node connects to the active node, the active synchronization services checks to see if there are too many updates for the standby; if so, the active synchronization service disconnects the standby node and generates the exception "Slave has xxxx bytes sqls to be processed since last disconnection, which exceeds current available memory on the master sync service. Slave node will be disconnected. Please run backup and restore to sync the master and slave nodes." As indicated in the message, run backup and restore to sync the active node. For more information, see Synchronizing the Active and Standby Repositories.
| File Name | Description |
|---|---|
| /etc/opt/teradata/datamover/sync.properties | Settings that the Data Mover Replication Service uses for synchronizing active with standby repositories. |
| /opt/teradata/datamover/sync/nn.nn/DMReplication.jar | Executable binary file used by the synchronization services. |
| /opt/teradata/datamover/sync/nn.nn/dmsync | Script for starting the synchronization service. |
Usage Notes
You can use the host name or IP address as values for the master.host and jobstore.host in sync.properties for the active and standby servers. When configuring the servers, use only host names or IP addresses. Do not mix host names and IP addresses.
| Scenario | Result |
|---|---|
| The sync.properties file is not located at /etc/opt/teradata/datamover | The synchronization service reports an error. |
| The dmsync or DMReplication.jar file is not located at /opt/teradata/datamover/daemon/nn.nn | The synchronization service reports an error. |
| The standby synchronization service is started before the active synchronization service | The synchronization service reports an error. |
| The active and standby synchronization services are started on the same server | The synchronization service reports an error. |
| The active repository is unavailable (offline, down, restarting) | The synchronization service stops all connected standby repositories. |
| The active repository is restarted after a period of unavailability | The synchronization service reports an error. The active sync service must be restarted by running /opt/teradata/datamover/sync/nn.nn/dmsync start, where nn.nn in the path refers to the major and minor version numbers of Data Mover. Previously connected standby services must be restarted individually by running /opt/teradata/datamover/sync/nn.nn/dmsync start for each one. |