Hi Jeroen,
Thanks for preparing the example, it made checking what the problem is very
simple :-)
Try searching for `confirmDelivery` in your code snippet. It's not there.
And with no confirmation, there is no information on in the sending-actor
that the target has really received the message.
The interaction MUST be such that:
[bob] [alice]
m(1) -------------X # message lost!
m(1) ------------------> got m(1) # message got here
X---------------- confirm 1 # confirmation lost!
# re-send triggers
m(1) -------------------> got m(1) # "oh, I know it already!"
confirmDelivery(1) <----- confirm 1 # confirmation got to sender
At least once delivery semantics imply two things:
1) the receiver must be ready to receive the message multiple times (should
simply ignore if it knows it already, or the messages should be idempotent
<http://en.wikipedia.org/wiki/Idempotence>).
2) the sender must retry sending a message until it gets a confirmation
back from the receiver
In your case you forgot the 2) rule.
AtLeastOnceDelivery has helpers for this, in form of: confirmDelivery.
Please read the example in the docs in detail:
http://doc.akka.io/docs/akka/snapshot/scala/persistence.html#at-least-once-delivery
I would also highly recommend watching my or Endre's talks which are
* "without past or present" by Endre
http://letitcrash.com/post/83823246588/without-past-and-present
* "distributed consensus aka. what do we eat for lunch" by me
http://letitcrash.com/post/98879157982/introduction-to-distributed-consensus-by-konrad
They have videos and slides, I hope you'll enjoy it (great watch right in
time for a friday evening?)!
Happy hakking!
--
Cheers,
Konrad 'ktoso' Malawski
hAkker @ Typesafe
<http://typesafe.com>
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