What is the difference between a transaction and completion message in a Daml trigger?

Questions
1

A trigger’s updateState function has the signature Message -> TriggerUpdateA s (). A Message can be a Transaction, Completion, or Heartbeat, which indicates that they’re mutually exclusive. However, Completion is the only message that includes a completion status.

For successful transactions, when would one receive a Completion rather than a Transaction?

And for a failed transaction, would one always receive a Completion rather than a Transaction?

1 Like
2

For a successful commands you will receive both a transaction and a completion. For failed commands you will only received a failded completion. Triggers just mirror the transaction service and completion service.

3

So for successful commands, updateState will be invoked twice?

4

Yes, you don’t get guarantees about the order just like you don’t get guarantees if you subscribe to the corresponding ledger API streams.

5

Thanks, it’s helpful to know that the semantics mirror the ledger API.