Modes of Stream Replication
You can replicate streams in one of two replication modes. You specify the mode per source-replica pair.
Asynchronous replication
In this replication mode, HPE Ezmeral Data Fabric Streams confirms to producers that messages are published after the messages are placed in partitions. Messages are replicated in the background. Therefore, the latency of message publishing is not affected by the time required for the network round trip between the source cluster and the destination cluster.
This type of replication is well-suited for clusters that are geographically separated in wide-area networks.
Asynchronous replication is the default replication mode.
Synchronous replication
In this replication mode, HPE Ezmeral Data Fabric Streams confirms to producers that messages have been placed in partitions only after the messages are sent to a gateway in the destination cluster.
Due to the confirmations that HPE Ezmeral Data Fabric Streams receives on source clusters, synchronous replication is especially well-suited for creating a backup of your data for disaster recovery.
When the latency of a replication stream is high, HPE Ezmeral Data Fabric Streams switches to asynchronous replication temporarily so that producers are not blocked indefinitely. After the latency is sufficiently reduced, HPE Ezmeral Data Fabric Streams switches back to synchronous replication.
The same switching from synchronous to asynchronous replication occurs if all gateways fail. HPE Ezmeral Data Fabric Streams does not resume synchronous replication until a new gateway is established or at least one of the failed gateways is restarted.