A database configured in an Availability Group might have different availability modes (synchronous-commit or asynchronous-commit). Databases using synchronous-commit mode are required for more investigations. In this mode “the secondary replica writes incoming log records to disk (hardens the log) and sends a confirmation message to the primary replica.”
The migration of the AGs infrastructure is a step-by-step process. When the migration of one VM to VMware Cloud on AWS is completed leaving the second VM on-premises, it’s expected that the latency reflected in the metrics Primary Replica Commit Time and Harden Time will increase.
The figure below represents time series data for the referenced metrics when both VMs are located within a single datacenter:
The figure below represents time series data when the VM hosting a secondary replica in synchronous-commit mode is migrated to the SDDC:
To avoid potential increased application latency, changing the database Availability Mode to asynchronous-commit during the migration may be required. This change will also require switching Failover mode to manual. If changing the Availability Mode isn’t possible, plan the migration to occur during the maintenance window or when load on the database is minimal.
