sijie opened a new issue #5476: Message deduplication is not well handled when batching is enabled with external provided sequenceId URL: https://github.com/apache/pulsar/issues/5476 **Describe the bug** Current implementation of Pulsar producer doesn't check the sequenceId when adding messages to a batch container. That results in violations to idempotent producing with external sequenceId. **To Reproduce** - provide 10 message with sequenceId from 0-9 - provide 10 message with sequenceId from 0-9 again - flush the producer - these 20 messages will be received by the consumer **Expected behavior** The second 10 messages will not be added to container, because they are duplicated. We can throw exceptions to client to indicate that it adds out-of-order sequence ids. **Additional context** There are a couple places requires attentions regarding handling batched messages with external sequenceId. 1) The logic to maintain `lastPublishedSequenceId` is incorrect when using external sequenceId : `lastSequenceIdPublished = op.sequenceId + op.numMessagesInBatch - 1;`. Because the last sequence id is an external sequence id, which can't be computed by adding the number of messages in the batch. 2) We only maintain `lastPublishedSequenceId` (which is the acked seequence id). We also need to maintain a `lastPushSequenceId` to indicate the last sequence id that a producer sends to the broker. 3) the broker need to handle the first sequence id and last sequence id in a message batch.
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