Dead letters incorrect processed for messages batch

[mprokushenkov]

Describe the bug
Producer produces 10 messages. Consumer with set deads letters policy acks 9 messages and 1 nacks. This will lead to all 10 messages coming to dead letters topic.

To Reproduce
I'm testing scenario where producer sents messages using batch. Consumer with enabled dead letters policy acks all messages but nacks one message. Then another consumer receives messages from dead letters topic.

Steps to reproduce the behavior:

1. Instanciate producer with enabled batching
2. Instanciate consumer with enabled dead letters policy (maxRedeliverCount should be equals 0)
3. Instanciate consumer for receiving messages from dead letters topic
4. Send 10 messages
5. Receive all messages and ack first 9 but nack for last (10)
6. Receive messages from dead letters queue

Expected behavior
I expect that only nacked (10) message will be received from dead letters queue.

Screenshots
Here is a screenshot of log messages produced by steps specified above:

In [Step 3] only last (10) message should be received.

Desktop (please complete the following information):

• OS: Windows
• Environment: docker
• Pulsar version: 2.4.1

Additional context
No additional context.

[jiazhai]

Looking from the code, currently dead letter not support batch messages very well. a batch is handled as a unit. This is more of an enhancement requirements. ping @codelipenghui to confirm.

[gmethvin]

I also noticed this after reporting essentially the same issue as #5969. I’d argue it’s a bug because the consumer APIs are defined on messages, not batches. At the very least it’s a bug because the documentation does not mention batches at all and suggests only the negatively acknowledged message will be redelivered. Even if the current behavior were correctly documented, though, it makes negative acknowledgements much less useful, as it puts an extra burden on the consumer of tracking duplicates.

[tisonkun]

Closed as stale. Please create a new issue if it's still relevant to the maintained versions.