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

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

    [ https://issues.apache.org/jira/browse/KAFKA-8755?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16900693#comment-16900693 ] 

Bruno Cadonna commented on KAFKA-8755:
--------------------------------------

In a first analysis, I narrowed down the issue to the setting of the offset limits in the following two code snippets.

{{AbstractTask#updateOffsetLimits()}}
{code:java}
final OffsetAndMetadata metadata = consumer.committed(partition);
final long offset = metadata != null ? metadata.offset() : 0L;
{code}

{{ProcessorStateManager#offsetLimit}}
{code:java}
final Long limit = offsetLimits.get(partition);
return limit != null ? limit : Long.MAX_VALUE;
{code}

Currently, my guess is that {{AbstractTask#updateOffsetLimits()}} is called during initialization and closing of the stand-by task but it is not called during normal processing. The reason is that during normal processing {{StandByTask#commit()}} is never called because the flag {{commitNeeded}} is never set to true. This occurs only for stand-by tasks for optimized source tables. Further investigation is needed to confirm my guess. 

> 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
>            Priority: Major
>              Labels: newbie
>         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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