intkuroky commented on PR #1411:
URL:
https://github.com/apache/pulsar-client-go/pull/1411#issuecomment-3268686801
> How could the out-of-order issue happen?
Yes, the sending operation is indeed executed within the same event loop.
However, the generation of sequenceID does not occur within this event loop.
This PR is precisely to move the sequenceID generation step into the same
event loop. It is precisely because the generation of sequenceID and message
sending are not both in the same event loop that this leads to potential
out-of-order issues.
For example:
`
producer, err := client.CreateProducer(pulsar.ProducerOptions{
BatchingMaxPublishDelay: time.Second, // Let the batch
operation occur after the single message operation
})
producer.SendAsync(context.Background(), &pulsar.ProducerMessage{
Payload: []byte("batch messages"),
}, func(id pulsar.MessageID, message *pulsar.ProducerMessage, err
error) {
// id: -1:-1:0
})
time.Sleep(5e8) // Ensure that genSingleMessageMetadataInBatch is
executed first with sequenceID set to 1
// 1. genSingleMessageMetadataInBatch ->
updateSingleMessageMetadataSeqID -> sequenceID = 1
producer.SendAsync(context.Background(), &pulsar.ProducerMessage{
Payload: []byte("single message"),
DeliverAt: time.Now(),
}, func(id pulsar.MessageID, message *pulsar.ProducerMessage, err
error) {
//
})
// 2. updateMetaData -> sequenceID = 2
// 3. publishing a single message (payload:"single message"
sequenceID:2)
// 4. 1s interval ticker fires -> Flushing batch messages
(payload:"batch messages" sequenceID:1)`
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