Progress Fathom Replication
User’s Guide

> ## Synchronous and asynchronous

> Fathom Replication supports two methods of replication: synchronous and asynchronous. Figure 1–6 shows a synchronous and an asynchronous method of replication.

> Figure 1–6: Synchronous and asynchronous configurations

> In Figure 1–6, the asynchronous replication supports a maximum of two Fathom Replication agents and the synchronous replication supports only one Fathom Replication agent. There is one Fathom Replication agent for every target database.

> During asynchronous operation, the user changes records and the transactions are committed without acknowledgement and sent back to the Fathom Replication server. Without waiting, the Fathom Replication server sends more AI blocks from the AI transaction log to the Fathom Replication agent, and the Fathom Replication agent applies these changes to the target database. Of the two configurations (synchronous and asynchronous), asynchronous performs better.

> Figure 1–7 shows asynchronous operation in the Fathom Replication model.

> Figure 1–7: Asynchronous operation

> During synchronous connection, the user changes records and the transactions are committed. When the Fathom Replication agent encounters a transaction end, it sends an acknowledgement back to the Fathom Replication server. The committing user will block until the transaction is fully applied to the target database. Other users are not blocked during this activity. Of the two configurations, synchronous is the safest. For more information on choosing asynchronous versus synchronous mode, see the "Hot standby" section.

> Figure 1–8 shows synchronous operation in the Fathom Replication model.

> Figure 1–8: Synchronous operation

> Because of the user blocks in the synchronous model, performance will be slower than in the asynchronous model.

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