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stephanos
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Jan 23, 2026
docs/encyclopedia/workflow-message-passing/handling-messages.mdx
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| #### Message IDs and handling Continue-As-New {#exactly-once-message-processing} | ||
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| Many developers want their message handlers to run exactly once--to be idempotent--in cases where the same Signal or Update is delivered twice or sent by two different call sites. Temporal deduplicates messages for you on the server, but there is one important case when you need to think about this yourself when authoring a Workflow, and one when sending Signals and Updates. | ||
| Usually, you'll want your message handlers to run exactly once--to be idempotent--in cases where the same Signal or Update is delivered twice. For Updates, Temporal handles this for you on the server, by deduplicating according to the Update ID. For Signals, you should use a custom idempotency key that you send as part of your own signal inputs, implementing the deduplication in your Workflow code. The Update ID is set automatically to a UUID, but you can set it yourself. |
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I'd move the last sentence about UUID next to the Update sentence. The Signal sentence breaks the flow there in the middle.
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It may be simpler to just ask people to check idempotency. And then explain the reasoning that it's necessary for signals and update plus CaN .
That way, if they add CaN later, they won't cause a bug. And I don't think there is much harm to a redundant check.
| See the links below for how to ensure handlers are finished in your SDK. | ||
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| #### Ensuring your messages are processed exactly once {#exactly-once-message-processing} | ||
| #### Message IDs and handling Continue-As-New {#exactly-once-message-processing} |
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I like that this is focused on CaN now. The part about the same Update/Signal coming in from different clients is now only implied. That might be fine.
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docs/encyclopedia/workflow-message-passing/handling-messages.mdx
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What does this PR do?
Clarifies the section on idempotency keys and CAN. There were reports that for the following sentence
it was not obvious that it referred to the situation when the workflow is using CAN.