Transaction log replay: The foundation for DAG replication

Within a DAG, transaction log data generated by the active database copy are streamed by the Replication service to each of the servers that maintain passive database copies, where the data are then reconstructed, validated, and replayed to update the passive copies. The DAG is the boundary of data replication for transaction logs. In other words, you cannot replicate logs to a server in a different DAG and have Exchange replay the logs into a database replica there. It then follows that before you can create a copy of a database, it must reside in a DAG, and the target server must be part of the same DAG. The DAG is also the boundary for failover insofar as failovers occur within the ...

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