{"id":"9bae647cb0ae2818","repo":"apache/kafka","slug":"there-are-insufficient-bytes-available-to-read-ass","errorCode":null,"errorMessage":"There are insufficient bytes available to read assignment from the sync-group response (actual byte size {}) , this is not expected; it is possible that the leader's assign function is buggy and did not return any assignment for this member, or because static member is configured and the protocol is buggy hence did not get the assignment for this member","messagePattern":"There are insufficient bytes available to read assignment from the sync-group response \\(actual byte size (.+?)\\) , this is not expected; it is possible that the leader's assign function is buggy and did not return any assignment for this member, or because static member is configured and the protocol is buggy hence did not get the assignment for this member","errorType":"exception","errorClass":"IllegalStateException","httpStatus":null,"severity":"error","filePath":"clients/src/main/java/org/apache/kafka/clients/consumer/internals/ConsumerCoordinator.java","lineNumber":401,"sourceCode":"        log.debug(\"Executing onJoinComplete with generation {} and memberId {}\", generation, memberId);\n\n        // Only the leader is responsible for monitoring for metadata changes (i.e. partition changes)\n        if (!isLeader)\n            assignmentSnapshot = null;\n\n        ConsumerPartitionAssignor assignor = lookupAssignor(assignmentStrategy);\n        if (assignor == null)\n            throw new IllegalStateException(\"Coordinator selected invalid assignment protocol: \" + assignmentStrategy);\n\n        // Give the assignor a chance to update internal state based on the received assignment\n        groupMetadata = new ConsumerGroupMetadata(rebalanceConfig.groupId, generation, memberId, rebalanceConfig.groupInstanceId);\n\n        SortedSet<TopicPartition> ownedPartitions = new TreeSet<>(COMPARATOR);\n        ownedPartitions.addAll(subscriptions.assignedPartitions());\n\n        // should at least encode the short version\n        if (assignmentBuffer.remaining() < 2)\n            throw new IllegalStateException(\"There are insufficient bytes available to read assignment from the sync-group response (\" +\n                \"actual byte size \" + assignmentBuffer.remaining() + \") , this is not expected; \" +\n                \"it is possible that the leader's assign function is buggy and did not return any assignment for this member, \" +\n                \"or because static member is configured and the protocol is buggy hence did not get the assignment for this member\");\n\n        Assignment assignment = ConsumerProtocol.deserializeAssignment(assignmentBuffer);\n\n        SortedSet<TopicPartition> assignedPartitions = new TreeSet<>(COMPARATOR);\n        assignedPartitions.addAll(assignment.partitions());\n\n        if (!subscriptions.checkAssignmentMatchedSubscription(assignedPartitions)) {\n            final String fullReason = String.format(\"received assignment %s does not match the current subscription %s; \" +\n                    \"it is likely that the subscription has changed since we joined the group, will re-join with current subscription\",\n                    assignment.partitions(), subscriptions.prettyString());\n            requestRejoin(\"received assignment does not match the current subscription\", fullReason);\n\n            return;\n        }\n","sourceCodeStart":383,"sourceCodeEnd":419,"githubUrl":"https://github.com/apache/kafka/blob/c31c9215e131f8c17e79f8901b48c13ee6aa8e7a/clients/src/main/java/org/apache/kafka/clients/consumer/internals/ConsumerCoordinator.java#L383-L419","documentation":"IllegalStateException thrown from ConsumerCoordinator.onJoinComplete (ConsumerCoordinator.java:401) when the assignment ByteBuffer returned by SyncGroup has fewer than 2 bytes — too small to encode even the version short. That means the leader's assignor produced no bytes for this member, or static membership (group.instance.id) handling delivered an empty buffer. The library treats this as a buggy assignor / protocol mismatch rather than a transient network fault.","triggerScenarios":"onJoinComplete receives assignmentBuffer.remaining() < 2. The leader's ConsumerPartitionAssignor.assign(...) returned an empty/null assignment for this member, or — under static membership — the cooperative protocol path produced an empty buffer for this member.","commonSituations":"Custom assignor that returns null or an empty Assignment under edge cases; leader threw inside assign() and the empty result propagated; static membership (group.instance.id) combined with a buggy cooperative protocol or a client-version mix inside the group; test/mock assignors that forget to populate the assignment.","solutions":["If running a custom ConsumerPartitionAssignor, ensure assign() always returns a non-empty Assignment that includes every member (serialize each member's slice via ConsumerProtocol.serializeAssignment).","When using group.instance.id (static membership), ensure all group members run the same fixed client version that supports it.","Inspect the leader consumer's logs for exceptions thrown during assign(); a buggy leader silently returning empty is the usual culprit.","Temporarily remove static membership to confirm whether the static-member protocol path is the trigger."],"exampleFix":null,"handlingStrategy":"try-catch","validationCode":null,"typeGuard":null,"tryCatchPattern":"try {\n    consumer.poll(Duration.ofSeconds(1));   // surfaces in onJoinComplete\n} catch (IllegalStateException e) {\n    if (e.getMessage().contains(\"insufficient bytes available\")) {\n        // leader's assign() returned an empty/buggy assignment; force a clean rejoin\n        consumer.unsubscribe();\n        consumer.subscribe(topics);\n    } else throw e;\n}","preventionTips":["If you ship a custom ConsumerPartitionAssignor, guarantee assign() returns a non-empty Assignment for EVERY member, including the leader.","Unit-test custom assignors under static membership (group.instance.id set) — that path commonly produces empty assignments.","Verify the leader receives the full member-id set in the SubscriptionMetadata before computing assignments.","Log memberIds your assignor saw so a missing assignment is diagnosable."],"tags":["consumer","assignor","rebalance","static-member"],"analyzedSha":"c31c9215e131f8c17e79f8901b48c13ee6aa8e7a","analyzedAt":"2026-08-03T12:34:05.770Z","schemaVersion":2}