Progress Fathom Replication
User’s Guide

> ## Fathom Replication agent

> For the Fathom Replication server to succeed in keeping the source and target database identical, it needs a Fathom Replication agent to receive information and perform updates to the target database. The Fathom Replication agent process receives configuration and operating instructions from the Fathom Replication server, including what actions to follow if connection to the Fathom Replication server is lost.

> Figure 1–4 shows the Fathom Replication agent process in the Fathom Replication model.

> Figure 1–4: Fathom Replication agent

> The Fathom Replication agent performs the actual process of updating the target database. The Fathom Replication agent must reside on the target database machine and provides the following services:

> - Updates the target database to keep it identical with the source database by using the AI blocks sent from the Fathom Replication server.

> - Performs a continuous roll forward of the source database to the target database.

> - Places the target database into Enhanced Read Only mode. For more information on Enhanced Read Only mode, see the "Enhanced Read-only mode" section. For information on what your product supports, see the "Database access once Fathom Replication is running" section.

> The Fathom Replication model with source and target, Fathom Replication server, and Fathom Replication agent, coexists with a standard database model with its servers, brokers, and other processes.

> Figure 1–5 illustrates the Fathom Replication model coexisting in a standard database environment.

> Figure 1–5: Fathom Replication model

> As shown in Figure 1–5, the source and target databases can be on the same machine. However, the source and target database should reside on separate machines so the target can run if the source machine fails.

> ##### Critical agent

> Fathom Replication allows a maximum of two agents per server.

> You can designate one agent as critical when you want to automatically transition to that agent’s target database during failure processing. For example, if you have two target databases, only the database managed by a critical agent (with `transition` set to `auto`) will automatically transition during failure processing.

> There can be, at most, one critical agent defined. If a second critical agent is configured, it will be changed to a noncritical agent. All agents by default are noncritical. To change an agent to critical, the `critical` property must be set to `1`.

> For more information, see the "Fathom Replication properties" section.

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