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https://issues.apache.org/jira/browse/KAFKA-8755?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16912669#comment-16912669
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Chris Pettitt commented on KAFKA-8755:
--------------------------------------
BUG 1 is interesting. The state restorer actually "restores" the changelog for
the DB, which is the input topic in the optimized case. Thus we actually have
all of the entries in the DB before we start and when we try to put our first
record we detect that the DB is actually ahead of the input topic.
> 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
> Assignee: Chris Pettitt
> 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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