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From "Tzu-Li (Gordon) Tai (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (FLINK-7143) Partition assignment for Kafka consumer is not stable
Date Sat, 22 Jul 2017 12:07:00 GMT

    [ https://issues.apache.org/jira/browse/FLINK-7143?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16097283#comment-16097283
] 

Tzu-Li (Gordon) Tai commented on FLINK-7143:
--------------------------------------------

Fixed for {{release-1.3}} in 3369cfe200bf2cb7ed04caf19d8599075e4cfe21.
This ticket should only be closed after related tests are merged to master.

> Partition assignment for Kafka consumer is not stable
> -----------------------------------------------------
>
>                 Key: FLINK-7143
>                 URL: https://issues.apache.org/jira/browse/FLINK-7143
>             Project: Flink
>          Issue Type: Bug
>          Components: Kafka Connector
>    Affects Versions: 1.3.1
>            Reporter: Steven Zhen Wu
>            Assignee: Tzu-Li (Gordon) Tai
>            Priority: Blocker
>             Fix For: 1.3.2
>
>
> while deploying Flink 1.3 release to hundreds of routing jobs, we found some issues with
partition assignment for Kafka consumer. some partitions weren't assigned and some partitions
got assigned more than once.
> Here is the bug introduced in Flink 1.3. 
> {code}
> 	protected static void initializeSubscribedPartitionsToStartOffsets(...) {
>                 ...
> 		for (int i = 0; i < kafkaTopicPartitions.size(); i++) {
> 			if (i % numParallelSubtasks == indexOfThisSubtask) {
> 				if (startupMode != StartupMode.SPECIFIC_OFFSETS) {
> 					subscribedPartitionsToStartOffsets.put(kafkaTopicPartitions.get(i), startupMode.getStateSentinel());
> 				}
>                 ...
>          }
> {code}
> The bug is using array index {{i}} to mod against {{numParallelSubtasks}}. if the {{kafkaTopicPartitions}}
has different order among different subtasks, assignment is not stable cross subtasks and
creates the assignment issue mentioned earlier. 
> fix is also very simple, we should use partitionId to do the mod {{if (kafkaTopicPartitions.get\(i\).getPartition()
% numParallelSubtasks == indexOfThisSubtask)}}. That would result in stable assignment cross
subtasks that is independent of ordering in the array.
> marking it as blocker because of its impact.



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