some of my users are attempting a pattern to deduplicate messages based on a time window instead of a fixed amount of space (a duplicate id cache)
so far the concept has been working very well. So they send their AMQP messages (qpid-jms-client) into a Last Value Queue with an appropriate identifier in the _AMQ_LVQ_NAME. They also set a TimeToLive on the message that is essentially the lag they will allow as they want to wait for possible duplicates. If any duplicates come in the Last Value Queue behavior is replacing the older message with the newer message until the expiration. expired messages are delivered to the preconfigured expiry queue where their application is listening. This is not perfect but its not intended to be. Its just intended to reduce additional unnecessary processing and they understand this is not a guarantee. It really helps with a system that produces messages in a way that has flurries of "notifications" about the same assetID over and over again. BUT where we are seeing is a problem is when we are consuming from the queue used to hold expired messages and we toss some exception and the message needs to be redelivered. the first time or two the message is redelivered it is delivered OK. But when the JMSXDeliveryCount is about 3 or 4 (we use redelivery delay and multipliers to spread these out) our qpid-jms-client stops being able to read the messages. we were only able to reproduce this when an AMQP message expired onto the queue. (expired from a LVQ in case that is relevant). if we place the message directly on a queue and test different exception and redelivery scenarios we cannot reproduce this behavior. i enable the qpid-jms-client frame logging (via env variable PN_TRACE_FRM=true) and i saw that in the situation when the client code cannot access the payload, even though the broker WAS still sending the payload. so i thought it was some odd issue with the client. The Apache Qpid team responded that the issue seems to be that the broker starts to send some ill formed payloads in this scenario. i dont want to repeat the stack traces and their response, you can read those here https://lists.apache.org/thread.html/b1fd9c09a1f66f5529601a8651fbb96585c011b22bbd84e07c4f23b1@%3Cusers.qpid.apache.org%3E would it be helpful if i tested that this happens if there is not a LVQ involved? i could have a message in a non-LVQ expire to another queue and see if redeliveries over their get messed up after a few attempts. For the record this is AMQP for producing and consuming. i do notice the messages waiting in the expiry queue have much more headers messages sent directly to a queue from client code. they seem to be headers full of information about the message as it left the previous queue. I tried to send a message directly to the expiry queue with all these headers to determine if it was the existence of one of these specifically that trigger the malformed frame but was not able to fully set all those headers. the JMSDeliverCount (type Long) was the one that the client would not let me set and as a result i could not test. for clarity thought i dont know that the issue exists due to a header that is just what i saw as a difference between messages be delivered to the queue by client code versus messages expiring from one queue to another. please look over the linked thread on the qpid list and let me know if you know why a message transfer fram would become malformed after a few failed deliveries only if the message expired onto the current queue. thanks so much
