Managing Offline Databases

SymmetricDS will continue to capture and retain changes for nodes that are not currently available on the network. This provides a great feature allowing full data sync recovery once the network is re-established. However, there is a trade-off in providing such a hands-off recovery option. The backlog of data being stored for all offline systems can grow indefinitely and slow down replication to healthy endpoints.

Managing these offline nodes becomes essential if they are common in your setup. Understanding how to best deal with them and recovery can keep your sync scenario healthy and performant. There are two factors to take into consideration when handling these offline scenarios.

Planned outages

If a node is not going to be available and it is planned for quite some time to be offline or maybe the location is permanently being shut down, this type of node should be unregistered completely from the system. Through the manage -> nodes screen select the node and on the registration button you can unregister the node directly to have it take an immediate effect and changes will no longer be gathered for that node and all existing eligible for purge immediately.

Unplanned outages

Turn on the “Watchdog” job to monitor for offline nodes and unregister them automatically if they pass a certain threshold setting. Setting up such a process ensures a healthy system that will not retain information for nodes that are no longer communicating.

1. Turn on the Watchdog job

2. Set the parameter that controls the threshold the Watchdog job utilizes.

Set the following parameter to a value greater than 0 that will server as your threshold of how long a node can be offline before it is automatically removed from the sync scenario.


NOTE: Check the frequency at which the heartbeat job runs to set this parameter accordingly. By default, the heartbeat job runs every 15 min so this parameter should be set to a value greater than the rate at which the job runs. The setting above would remove a node after 2 hours if no heartbeats were received.