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Status

Current state: Draft

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By maintaining a separate committedVoterSet, the system ensures:

• Safety: Quorum checks and leader decisions are based on a membership configuration that is guaranteed to be replicated and agreed upon by a majority.

• Stability: The committed voter set changes only at commit points, avoiding transient or rolled-back configurations.

• Both committed and uncommitted voters participate in quorum decisions and elections. However, uncommitted voters (those whose VotersRecord has been appended but not yet committed) carry a risk: if the leader crashes before the VotersRecord is committed, the voter change maybe lost due to log truncation, leading to potential configuration inconsistencies.

• Stability: When the committed and uncommitted voter sets differ, the cluster is in a joint consensus phase.
  Exposing this state allows management and orchestration systems to recognize that the controller quorum is undergoing a transitional reconfiguration, and to avoid assuming the new configuration is already stable.

• Debugging and Compliance Verification: During troubleshooting or post-incident audits, operators and tools must be able to differentiate between committed voters and uncommitted voters that have started replicating but are not yet officially part of the quorum.This distinction is critical for confirming whether a reconfiguration completed successfully and whether the cluster’s control plane reached a consistent stateCorrectness under Reconfiguration: Both during joint consensus transitions and simple add/remove operations, the system preserves Raft’s safety guarantees.

Public Interfaces

Request Schema

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The leaderState is extended to reference the KRaftControlRecordStateMachine, from which derives the high watermarkvoter set history. Using this information the of high watermark from LeaderState, the committed voter set can be obtained directly from KRaftControlRecordStateMachine. Both the voter set in the KRaftControlRecordStateMachine and the high watermark are maintained entirely in memory. This eliminates disk I/O , there by, and minimizing performance impact.

Semantic

The relationship between voters and committed voters is defined as follows:

Committed voter present in current voters/observers
If a committed voter is also present in the current voters or observers set, its ReplicaState is identical to the corresponding entry in those sets. This ensures that all runtime fields within ReplicaState are available.Committed voter absent from voters or observers available and reflect the current replica state.

Committed voter absent from voters or observers
If a committed voter is not found in either voters or observers, certain runtime-specific fields cannot be derived, since the replica is no longer actively participating in log replication. To maintain schema consistency, these fields in its ReplicaState are set to sentinel values:

• hasAcknowledgedLeader = false

• endLogOffset = -1

• lastFetchTimestamp = -1

• lastCaughtUpTimestamp = -1

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Above fields are only meaningful for active replicas(voter) in the quorum. For committed voters, they are not strictly required—the sentinel values simply indicate that the data is unavailable or not applicable.

Benefit

This mechanism strengthens the Raft membership model by:

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Making committed membership explicit.

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Providing a consistent interface for tooling and client introspection.

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Improving the overall transparency and debuggability of the cluster state.

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High watermark is unknown when a new leader is elected 

• In such case, the empty set should be returned because we don't know the high watermark.
• Committed voters can be returned as non-empty when leader update the high watermark.

Compatibility, Deprecation, and Migration Plan

• Bump DescribeQuorumRequest and DescribeQuorumResponse to a newer version, with backward compatibility preserved for the old protocol version.

Test Plan

• Unit test and integration test will be added.

Rejected Alternatives

• A new field, state, can be introduced within the ReplicaState structure to explicitly track the committed status of the voter like uncommitted and committed.