[jira] [Created] (KAFKA-8279) Discrepancy around what SubscriptionState.allConsumed returns

["Kevin (JIRA)" <ji...@apache.org>]

Kevin created KAFKA-8279:
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             Summary: Discrepancy around what SubscriptionState.allConsumed returns
                 Key: KAFKA-8279
                 URL: https://issues.apache.org/jira/browse/KAFKA-8279
             Project: Kafka
          Issue Type: Bug
          Components: clients
    Affects Versions: 2.0.1
            Reporter: Kevin


Per [https://kafka.apache.org/22/javadoc/index.html?org/apache/kafka/streams/KafkaStreams.html], the "position" offset is $latest_offset_customer_has_seem_from_poll + 1; i.e., it is the offset of the next message the consumer will see. If this is the case though, there would be a bug - both KafkaConsumer and MockConsumer on v2.2 and v2.0.1 (my version) have 'commitSync' methods that are:

'commitOffsetsSync(subscriptions.allConsumed(), timeout.toMillis())'

This would mean that each commit actually commits one message per owned partition that the consumer has yet to see. This wouldn't be a problem under normal operation as the consumer would still get that message on its next poll, but if the consumer were to die between the commitSync and the next poll then it would restart and skip that message. This would be a pretty serious bug!

However, digging into SubscriptionState itself, I see:
{code:java}
* Once assigned, the partition is not considered "fetchable" until its initial position has
* been set with {@link #seek(TopicPartition, long)}. Fetchable partitions track a fetch
* position which is used to set the offset of the next fetch, and a consumed position
* which is the last offset that has been returned to the user{code}
Implying that the "position" offset is actually the last position returned to the user, which would make the bug only in MockConsumer which sets its subscriptions.position to be $highest_offset_seen + 1.

Which meaning do we expect "position" to be?



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