Hi, I’m using the qpid-proton C++ library and receiving messages via this component: https://qpid.apache.org/releases/qpid-proton-0.30.0/proton/cpp/api/classproton_1_1messaging__handler.html In the on_container_start method, I used the idle_timeout connection option to define some time after which the connection should be dropped if there was no heartbeat messages transferred between my app and the broker. The following scenario can happen:
1. My app is down. 2. Let’s say 2 messages accumulate in the broker: message A and message B. 3. My app comes online. 4. My app processes message A from the broker in its proton::messaging_handler:: on_message override method. However, processing this message takes longer than the idle_timeout defined above. 5. My app processes message B from the broker. 6. Because of the long processing time of message A (point 4 above), the on_transport_error method is invoked with an “amqp:resource-limit-exceeded: local-idle-timeout expired” error. 7. Container execution stops because of the error above. 8. My app starts the container again. 9. My app receives messages A and B again. These are undesirable duplicates that the app has already processed in points 4-5. My aim is to eliminate the duplicate messages in point 9. I tried the following: 1. I could use a local cache where I store the message ids that my app has already processed. I don’t really want to do this, because this cache might grow arbitrarily large. In my scenario above, I used 2 messages (A and B) but in practice an arbitrarily large number of duplicates may arrive. I would be okay with a solution that implies a constant number of messages (preferably 0 or 1) is duplicated. 2. I could use at-most-once delivery mode. I can’t afford this, because then I would lose messages if my app crashes while processing a message. 3. I could use exactly-once delivery-mode. I saw this mentioned in the docs<https://qpid.apache.org/releases/qpid-proton-0.30.0/proton/cpp/api/overview_page.html>, but I couldn’t exactly find how to set this on the API. The necessary option seems to be missing from the relevant enum: https://github.com/apache/qpid-proton/blob/master/cpp/include/proton/delivery_mode.hpp#L33 4. I tried using at-least-once delivery mode with explicitly calling proton::delivery::accept() and proton::delivery::settle() in the proton::messaging_handler:: on_message override. Unfortunately, this still resulted in duplicates. This suggests that messages are not actually settled synchronously when I’m calling accept() or settle(). I suspect that the attempt to settle the message is placed in some sort of a queue whose processing is then aborted due to the call to on_transport_error and the subsequent container stop. The above (especially point 4) suggests that my problem of duplicate messages could be solved by having a way of synchronously settling deliveries inside the proton::messaging_handler:: on_message override. Is this possible somehow? Thanks a lot! Attila The information contained in this email is strictly confidential and for the use of the addressee only, unless otherwise indicated. If you are not the intended recipient, please do not read, copy, use or disclose to others this message or any attachment. Please also notify the sender by replying to this email or by telephone (+44 (0)20 7896 0011) and then delete the email and any copies of it. Opinions, conclusions (etc) that do not relate to the official business of this company shall be understood as neither given nor endorsed by it. IG Group Holdings plc is a company registered in England and Wales under number 04677092. VAT registration number 761 2978 07. Registered Office: Cannon Bridge House, 25 Dowgate Hill, London EC4R 2YA. Listed on the London Stock Exchange. Its subsidiaries IG Markets Limited and IG Index Limited are authorised and regulated by the Financial Conduct Authority (IG Markets Limited FCA registration number 195355 and IG Index Limited FCA registration number 114059). IG Europe GmbH is authorised and regulated by the Bundesanstalt für Finanzdienstleistungsaufsicht (BaFin registration number 148759) and the Deutsche Bundesbank. The Swedish branches of IG Markets Ltd and IG Europe GmbH are regulated by the Finansinspektionen.-
