José Armando García Sancio created KAFKA-20740:
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Summary: It is possible to have more hand one concurrent voter
change operation
Key: KAFKA-20740
URL: https://issues.apache.org/jira/browse/KAFKA-20740
Project: Kafka
Issue Type: Bug
Components: kraft
Affects Versions: 4.0.0
Reporter: José Armando García Sancio
Assignee: José Armando García Sancio
KRaft maintains an invariant where only a single voter change operation can be
pending at any given time. This operation is restricted to a single
modification—one addition, removal, or update—relative to the committed voter
set. This constraint is essential to prevent split-brain scenarios or
inconsistencies, ensuring that a majority of voters in both the old and new
configurations have committed to and agree upon the change.
Currently, KRaft violates this invariant by relying on the change voter handler
state to enforce the single-pending-operation rule. A problem arises when an
operation times out while the KRaft control records are still residing in the
log or batch accumulator; in these instances, KRaft may incorrectly reset the
change voter handler state.
To resolve this, the code must be modified so that the change voter handler
state is not reset once KRaft control records have been dispatched to the batch
accumulator. Following that dispatch, the state should only be reset through
replication, specifically via High Watermark (HWM) advancement.
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