Progress Fathom Replication
User’s Guide

> ## Fathom Replication failure processing

> If a failure does occur, such as a lost TCP/IP connection between the Fathom Replication server and the Fathom Replication agent, failure processing starts. If a failure occurs on the Fathom Replication server, it starts a process known as failure recovery. If a failure occurs on the Fathom Replication agent, it starts a process known as transition. For Fathom Replication to continue normal operations after a failure and after establishing connection again, the Fathom Replication server and the Fathom Replication agent must perform synchronization.

> This section documents synchronization, failure recovery, and transition.

> ##### Synchronization

> Synchronization is the process performed by the Fathom Replication server and the Fathom Replication agent to ensure that the target database and source database are identical. Synchronization is performed during database and replication startup and during failure recovery processing.

> ##### Failure recovery

> Failure recovery is the process that the Fathom Replication server performs after a communication failure with the Fathom Replication agent. During failure recovery, the Fathom Replication server attempts to reconnect to Fathom Replication agent or agents that have lost connection with the Fathom Replication server. After connection is re-established, the Fathom Replication server and Fathom Replication agent attempt to synchronize. Once synchronization is complete, normal operations resume.

> If the operation is unsuccessful, the Fathom Replication server will remove the failed Fathom Replication agent from its list of Fathom Replication agents to replicate to. If all Fathom Replication agents fail and connection cannot be established, the Fathom Replication server will stops. If the server stops, source databases activities continue and AI extents continue to fill.

> ##### Transition

> Transition is the action that the Fathom Replication agent performs after a communication failure has occurred with the Fathom Replication server. Within the `transition-timeout` value (as defined in the Fathom Replication server properties file), the Fathom Replication agent listens for connection requests from the Fathom Replication server. After connection is established, the Fathom Replication server and Fathom Replication agent perform synchronization. Once synchronization is complete, normal operations resume.

> If the Fathom Replication agent does not receive a communication attempt within the `transition-timeout` value, and auto transition has been configured, the target database is transitioned into a normal Progress database. If manual transition has been configured, the Fathom Replication agent will continue to wait for connection until manual transition is performed using `DSRUTIL` or the database is shut down.

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