apache/kafka · error · SchemaException

Unsupported assignment version: {}

Error message

Unsupported assignment version: {}

What it means

Thrown by ConsumerProtocol.checkAssignmentVersion() when the supplied assignment version is below ConsumerProtocolAssignment.LOWEST_SUPPORTED_VERSION. Older assignment wire formats are not supported; newer ones are accepted and silently capped to HIGHEST_SUPPORTED_VERSION, so this fires only for versions that predate the supported floor.

Source

Thrown at clients/src/main/java/org/apache/kafka/clients/consumer/internals/ConsumerProtocol.java:226

        }
    }

    public static ConsumerProtocolAssignment deserializeConsumerProtocolAssignment(final ByteBuffer buffer) {
        return deserializeConsumerProtocolAssignment(buffer, deserializeVersion(buffer));
    }

    private static short checkSubscriptionVersion(final short version) {
        if (version < ConsumerProtocolSubscription.LOWEST_SUPPORTED_VERSION)
            throw new SchemaException("Unsupported subscription version: " + version);
        else if (version > ConsumerProtocolSubscription.HIGHEST_SUPPORTED_VERSION)
            return ConsumerProtocolSubscription.HIGHEST_SUPPORTED_VERSION;
        else
            return version;
    }

    private static short checkAssignmentVersion(final short version) {
        if (version < ConsumerProtocolAssignment.LOWEST_SUPPORTED_VERSION)
            throw new SchemaException("Unsupported assignment version: " + version);
        else if (version > ConsumerProtocolAssignment.HIGHEST_SUPPORTED_VERSION)
            return ConsumerProtocolAssignment.HIGHEST_SUPPORTED_VERSION;
        else
            return version;
    }
}

View on GitHub (pinned to c31c9215e1)

Solutions

1. Print the offending version to determine whether it is a true legacy value or the symptom of corrupted/zeroed header bytes.
2. Read old snapshots with a Kafka version contemporaneous with the data; do not force-cross LOWEST_SUPPORTED_VERSION.
3. If the version came from the wire, check that the SyncGroup response was not truncated or replaced with garbage (look for BufferUnderflowException-adjacent logs).
4. Re-serialize via ConsumerProtocol.serializeAssignment(assignment) with no explicit version to pick up the current floor/ceiling.

Example fix

// before
ConsumerProtocol.serializeAssignment(a, (short) 0);

// after
ConsumerProtocol.serializeAssignment(a); // picks HIGHEST_SUPPORTED_VERSION

import org.apache.kafka.common.message.ConsumerProtocolAssignment;

static short ensureSupportedAssignmentVersion(short version) {
    if (version < ConsumerProtocolAssignment.LOWEST_SUPPORTED_VERSION)
        throw new IllegalArgumentException(
            "assignment version " + version + " below lowest supported "
            + ConsumerProtocolAssignment.LOWEST_SUPPORTED_VERSION);
    return (short) Math.min(version, ConsumerProtocolAssignment.HIGHEST_SUPPORTED_VERSION);
}

static boolean isSupportedAssignmentVersion(short v) {
    return v >= ConsumerProtocolAssignment.LOWEST_SUPPORTED_VERSION
        && v <= ConsumerProtocolAssignment.HIGHEST_SUPPORTED_VERSION;
}

try {
    ConsumerProtocol.serializeAssignment(assignment, version);
} catch (org.apache.kafka.common.protocol.types.SchemaException e) {
    log.error("Unsupported consumer protocol assignment version", e);
    throw e;
}

When it happens

Trigger: Calling ConsumerProtocol.serializeAssignment, deserializeAssignment, or deserializeConsumerProtocolAssignment with an explicit version below LOWEST_SUPPORTED_VERSION. Most often seen when a corrupted assignment header deserializes to version 0, or when custom code passes a stale hardcoded version constant.

Common situations: Persisted group-state snapshots from a much older Kafka being read by a current client; truncated/zeroed assignment bytes producing version 0; custom assignor hardcoding a version literal that has since been retired.

Related errors

• Malformed consumer protocol assignment
• Unsupported subscription version: {}
• Buffer underflow while parsing consumer protocol's header
• Malformed consumer protocol subscription
• Buffer underflow while parsing response for request with hea

AI-assisted analysis of apache/kafka@c31c9215e1 (2026-08-03). Data as JSON: /data/errors/6191a98cbf66ecad.json. Report an issue: GitHub.