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Question: at-least-once delivery #228

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drauch opened this Issue Mar 22, 2016 · 3 comments

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drauch commented Mar 22, 2016

According to the documentation NATS guarantees at-most-once delivery of a message, however, at-least-once delivery is not guarnateed.

I can iamgine only two scenarios where at-least-once delivery fails:

  • subscriber is not reachable anymore
  • subscriber cannot process the high load anymore

Both scenarios should lead to a forceful subscriber disconnect by the server.

Therefore, does the following assumption hold in general?

If at-least-once delivery cannot be fulfilled for a given subscriber, the subscriber is forcefully disconnected by the server.

Or the other way round:

As long as a subscriber is connected, he is guaranteed to receive all messages at-least-once and at-most-once (and in-order, if there is only a single publisher).

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derekcollison Mar 22, 2016

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Neither will hold when publisher and subscriber are connected to different servers in a cluster and the route between the servers is partitioned.

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derekcollison commented Mar 22, 2016

Neither will hold when publisher and subscriber are connected to different servers in a cluster and the route between the servers is partitioned.

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The only statement we can make is the following.

For any given publisher, messages produced will be delivered in order with at most-once delivery semantics per subscriber.

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derekcollison commented Mar 22, 2016

The only statement we can make is the following.

For any given publisher, messages produced will be delivered in order with at most-once delivery semantics per subscriber.

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drauch Mar 22, 2016

I understand, thank you for your clarification.

drauch commented Mar 22, 2016

I understand, thank you for your clarification.

@drauch drauch closed this Mar 22, 2016

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