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- Received messages don't require re-serialization before replication (they are received in serialized form)
- Received messages can be replicated in parallel with the execution of business logic which can effectively reduce the storage cost overhead to 0.zero!
While the premise behind Event Sourcing is simple, it requires discipline on the part of the application developer to ensure that no business logic decisions are made based on any data but that in the inbound messages and the state generated by those message to date, otherwise it would lead to divergent state on the primary and backup members. For example, something as simple as making a logical decision based on System.currentTimeMillis() could lead to the primary instance accepting an order and a backup instance rejecting an order as stale because of clock skew. In the event that the primary instance fails, the order would then not exist on the backup.
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