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https://issues.apache.org/jira/browse/FLINK-21317?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Piotr Nowojski updated FLINK-21317:
-----------------------------------
Fix Version/s: (was: 1.16.0)
> Downstream keyed state not work after FlinkKafkaShuffle
> -------------------------------------------------------
>
> Key: FLINK-21317
> URL: https://issues.apache.org/jira/browse/FLINK-21317
> Project: Flink
> Issue Type: Bug
> Components: Connectors / Kafka
> Affects Versions: 1.13.0
> Reporter: Kezhu Wang
> Priority: Minor
> Labels: auto-deprioritized-major
>
> {{FlinkKafkaShuffle}} uses
> {{KeyGroupRangeAssignment.assignKeyToParallelOperator}} to assign partition
> records to kafka topic partition. The assignment works as follow:
> # {{KeyGroupRangeAssignment.assignToKeyGroup(Object key, int
> maxParallelism)}} assigns key to key group.
> # {{KeyGroupRangeAssignment.computeOperatorIndexForKeyGroup(int
> maxParallelism, int parallelism, int keyGroupId)}} assigns that key group to
> operator/subtask index.
> When kafka topic partitions are consumed, they are redistributed by
> {{KafkaTopicPartitionAssigner.assign(KafkaTopicPartition partition, int
> numParallelSubtasks)}}. I copied code of this redistribution here.
> {code:java}
> public class KafkaTopicPartitionAssigner {
> public static int assign(KafkaTopicPartition partition, int
> numParallelSubtasks) {
> int startIndex =
> ((partition.getTopic().hashCode() * 31) & 0x7FFFFFFF) %
> numParallelSubtasks;
> // here, the assumption is that the id of Kafka partitions are always
> ascending
> // starting from 0, and therefore can be used directly as the offset
> clockwise from the
> // start index
> return (startIndex + partition.getPartition()) % numParallelSubtasks;
> }
> }
> {code}
> This partition redistribution breaks prerequisites for
> {{DataStreamUtils.reinterpretAsKeyedStream}}, that is key groups are messed
> up. The consequence is unusable keyed state. I list deepest stack trace
> captured here:
> {noformat}
> Caused by: java.lang.NullPointerException
> at
> org.apache.flink.runtime.state.heap.StateTable.transform(StateTable.java:205)
> at
> org.apache.flink.runtime.state.heap.HeapReducingState.add(HeapReducingState.java:100)
> {noformat}
> cc [~ym] [~sewen] [~AHeise] [~pnowojski]
> Below is my proposed changes:
> * Make assignment between partition and subtask customizable.
> * Provide a 0-based round-robin assignment. (This is making {{startIndex}} 0
> in existing assignment algorithms.)
> I saw FLINK-8570, above changes could be helpful if we finally decide to
> deliver FLINK-8570.
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