Progress Fathom Replication
User’s Guide

> ## Fathom Replication startup and initialization process

> During the Fathom Replication startup and initialization process, the Fathom Replication server attempts to contact the Fathom Replication agent through the target database broker on the port specified in the `control-agent` section of the source database replication properties file. Once the Fathom Replication server makes contact with the Fathom Replication agent, a handshaking process takes place. During this process, Fathom Replication:

> - Determines if the source and target databases are identical.

> - Verifies that the target database was created from the source database.

> - Performs synchronization.

> - Allows database connections.

> If the `defer-agent-startup` property is set to a valid non-zero value, source database activity is allowed once the source database is started. Source database activity will not halt until the very end of the synchronization process, when the Fathom Replication server completes the synchronization process. When synchronization is completed, it will reinsert itself back into the AI Block write process, where Progress RDBMS will be unblocked and normal database and Fathom Replication activity will continue.

> Before synchronization begins, if the Fathom Replication server cannot connect to its configured agent(s) on the first connection attempt, it will go into a Deferred Agent Startup. While in this state, the Fathom Replication server will wait five minutes, then attempt Fathom Replication agent connection again. The Fathom Replication server will remain in this state until all agent(s) are connected or until the time-out specified in the `defer-agent-startup` expires. Once all the agents are connected to, startup, initialization, and synchronization are performed. If you do not want to wait for the five minute intervals between connection attempts to the agent(s), you can force agent connection using the `DSRUTIL` function `startAgent`.

> Schema updates are not allowed while the Fathom Replication server is performing synchronization. If schema updates are being performed when failure recovery synchronization begins, source database updates will block until failure recovery is complete.

> Source database activity cannot continue without the agent(s) connected when synchronous replication is being used.

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