Kezhu Wang created FLINK-21317:
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Summary: 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
{{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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