Kevin created KAFKA-8279:
----------------------------
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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