Nico Habermann created KAFKA-12775:
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Summary: StreamsPartitionAssignor / ClientState throws an
exception when a new Task gets added to a KStreams Application in a
Backwards-Compatible Topology Change
Key: KAFKA-12775
URL: https://issues.apache.org/jira/browse/KAFKA-12775
Project: Kafka
Issue Type: Bug
Reporter: Nico Habermann
KAFKA-6145 added an [exception if the new High Availability Assignor tries to
look up the lag for a TaskId that seemingly does not
exist|https://github.com/apache/kafka/blob/trunk/streams/src/main/java/org/apache/kafka/streams/processor/internals/assignment/ClientState.java#L325].
I believe this is a functional regression.
Before, it was possible for Streams users to make backwards-compatible topology
changes and roll those out, without having to do a complete restore or reload.
For example:
Existing sample topology:
{code:java}
stream1 = stream(topic)
stream1
.map(...)
.to(output){code}
And doing this backwards-compatible change:
{code:java}
stream1 = stream(topic)
++ table = stream(topic2).through(repartition-topic)/repartition().toTable()
stream1
.map(...)
++ .join(table)
.to(output){code}
This effectively creates a new subtopology with a new task for the table
repartition.
In older KStreams versions, it would have been possible to simply roll this
change out.
Since 2.6, rolling this out will crash the stream because the linked exception
gets thrown when StreamsPartitionAssignor#getPreviousTasksByLag tries to look
up the lag for the new table-repartition-task
At this time, the only possible way to avoid this exception seems to be
deleting all local state and doing a complete restore with the new topology
change included.
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