aeron-io/aeron · info · ClusterEvent

Truncating Cluster Log - memberId=

Error message

Truncating Cluster Log - memberId=${memberId} state=${state} this.logLeadershipTermId=${logLeadershipTermId} this.leadershipTermId=${leadershipTermId} this.candidateTermId=${candidateTermId} this.commitPosition=${commitPosition} this.logPosition=${logPosition} this.appendPosition=${appendPosition} oldPosition=${oldPosition} newPosition=${newPosition}

What it means

ClusterEvent thrown by Election.onTruncateLogEntry after the follower's local log has been truncated back to newPosition via consensusModuleAgent.truncateLogEntry. It is an informational marker recording full election state (memberId, terms, positions) at the moment the log was rolled back, typically when a follower discovers the leader's log diverges from its own. The truncation has already been applied; this exception communicates the state transition.

Solutions

Inspect the log lines preceding this event to confirm truncation was expected; no action is needed if the cluster recovers and elects normally
If truncation loops repeatedly, verify all members share the same recording log directory and aeron.cluster.dir configuration
Check that the recording log (cluster-mark.mark / segment files) was not manually copied or restored from a different cluster
Upgrade to the latest Aeron patch release; election truncation edge cases have been fixed over time

Defensive patterns

Strategy: try-catch

Try / catch

// Election runs inside the cluster container; catch at service level if embedding
catch (ClusterEvent e) {
    // informational: log truncation already applied; monitor and let election continue
    LOG.info("Election log truncation event: {}", e.getMessage());
}

Prevention

Never manually copy recording logs between cluster members
Keep all members on the same Aeron version
Monitor election events in logs to detect repeated truncation loops

When it happens

Trigger: A follower in an election receives a NEW_LEADERSHIP_TERM event whose logPosition/appendPosition is behind what it has already appended, so onNewLeadershipTerm calls onTruncateLogEntry to roll its local recording log back to the leader's position.

Common situations: Cluster recovery after a leader crash where the previous leader committed entries that the new leader never had; split-brain residue; rejoining a stale member with a longer log than the elected leader.

Understand the failure class

Background: "Invalid state transition" errors: "status must be X, actually Y", "already rejected/charging/uninstalled", "cannot ... while running" — what they mean when a library rejects your call — this error's family across 31 libraries.

AI-assisted analysis of aeron-io/aeron@6d60124e15 (2026-09-12). Data as JSON: /api/errors/4f8724d23a99a8fa. Report an issue: GitHub.

Appendix: source

Thrown at aeron-cluster/src/main/java/io/aeron/cluster/Election.java:636

        final long appendPosition,
        final long oldPosition,
        final long newPosition)
    {
        ClusterTracing.traceOnTruncateLogEntry(
            memberId,
            state,
            logLeadershipTermId,
            leadershipTermId,
            candidateTermId,
            commitPosition,
            logPosition,
            appendPosition,
            oldPosition,
            newPosition);

        consensusModuleAgent.truncateLogEntry(logLeadershipTermId, newPosition);
        this.appendPosition = newPosition;
        throw new ClusterEvent("Truncating Cluster Log - memberId=" + memberId +
            " state=" + state +
            " this.logLeadershipTermId=" + logLeadershipTermId +
            " this.leadershipTermId=" + leadershipTermId +
            " this.candidateTermId=" + candidateTermId +
            " this.commitPosition=" + commitPosition +
            " this.logPosition=" + logPosition +
            " this.appendPosition=" + appendPosition +
            " oldPosition=" + oldPosition +
            " newPosition=" + newPosition);
    }

    long notifiedCommitPosition()
    {
        return notifiedCommitPosition;
    }

    private int init(final long nowNs)
    {

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