Progress Fathom Replication
User’s Guide

> ## Normal target database activity

> During normal operations, the Fathom Replication agent is performing a continuous roll forward. All database activity performed on the source database is applied to the target database in this manner. The Fathom Replication agent receives an AI block from the Fathom Replication server and applies the AI transaction log records to the target database. This process continues until the source or target database is shut down.

> This continuous roll forward is shown in Figure 2–2.

> Figure 2–2: Continuous roll forward on agent

> For the most part, the Fathom Replication agent performs no specific action for individual transaction log records other than applying them to the target database, as Figure 2–2 shows. However, there are exceptions. The Fathom Replication agent does special processing for the following transaction log records:

> - Checkpoint

> - AI extent switch

> - Transaction end

> Both a checkpoint and an AI extent switch cause the Fathom Replication agent to inform the Fathom Replication server that a synchronization point, commonly known as a sync point, has been encountered. A sync point instructs the Fathom Replication server that this is the point to begin synchronization during database startup or failure recovery.

> When synchronous replication is in effect, any process ending a transaction either by committing or rolling back will block or wait until the transaction end is processed by the Fathom Replication agent. After the Fathom Replication agent applies the transaction end, it informs the Fathom Replication server, and the Fathom Replication server unblocks the waiting process.

> The sync point and all other information needed for synchronization is stored in a file called `database``.repl.recovery`, where `database` is the name of your source or target database. Do not edit this file. This file must be deleted whenever the source or target database is restored, or Fathom Replication is re-enabled.

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