Progress Fathom Replication
User’s Guide

> ## Source and target

> Fathom Replication makes a copy of one database onto another and keeps those two databases identical, as seen in Figure 1–1.

> Figure 1–1: Fathom Replication from one site to another

> In Figure 1–1, one database must be considered the source and the other the target. The source database is the database that can be updated by users. The source database:

> - Is where users do their work and make their database updates.

> - Has both write access and read access.

> - Is not considered a source database until it is enabled as a Fathom Replication source database.

> - Is the database from which the Fathom Replication server replicates data to the target database.

> - Must have after-imaging activated.

> - Uses After Image (AI) to capture all database activity performed. This activity is then sent to the target database.

> The target database is an identical copy of the source database. A second target database can be set up for additional redundancy. The target database:

> - Originates from the source database and contains the same data, schema, and logical structure as the source database.

> - Does not allow database updates by anything other than Replication.

> - Permits queries and reports by users, as well as any non-database write activity (database utilities, for example) if Fathom Replication Plus is installed. For information on what your product supports, see the "Database access once Fathom Replication is running" section. See the "Utilities and Fathom Replication" section for supported non-database write activity.

> - Is updated solely by the Fathom Replication agent.

> Figure 1–2 shows the source and target database in the Fathom Replication model.

> Figure 1–2: Source and target database

> Note: The source and target database should reside on separate machines so the target can run if the source machine fails.

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