[jira] [Created] (KAFKA-8755) Stand-by Task of an Optimized Source Table Does Not Write Anything to its State Store

["Bruno Cadonna (JIRA)" <ji...@apache.org>]

Bruno Cadonna created KAFKA-8755:
------------------------------------

             Summary: Stand-by Task of an Optimized Source Table Does Not Write Anything to its State Store
                 Key: KAFKA-8755
                 URL: https://issues.apache.org/jira/browse/KAFKA-8755
             Project: Kafka
          Issue Type: Bug
          Components: streams
    Affects Versions: 2.4.0
            Reporter: Bruno Cadonna
         Attachments: StandbyTaskTest.java

With the following topology:

{code:java}
builder.table(
    INPUT_TOPIC, 
    Consumed.with(Serdes.Integer(), Serdes.Integer()), 
    Materialized.<Integer, Integer, KeyValueStore<Bytes, byte[]>>as(stateName)
)
{code}

and with topology optimization turned on, Kafka Streams uses the input topic {{INPUT_TOPIC}} as the change log topic for state store {{stateName}}. A stand-by task for such a topology should read from {{INPUT_TOPIC}} and should write the records to its state store so that the streams client that runs the stand-by task can take over the execution of the topology in case of a failure with an up-to-date replica of the state.

Currently, the stand-by task described above reads from the input topic but does not write the records to its state store. Thus, after a failure the stand-by task cannot provide any up-to-date state store and the streams client needs to construct the state from scratch before it can take over the execution.

The described behaviour can be reproduced with the attached test.



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