Kafka Fetch Response Wire Format v6

What is Fetch?

Consumers and follower replicas both issue this continuously for log replication and consumption. When a consumer's fetch stalls with empty responses despite records existing, check isolation.level: read_committed consumers are blocked by open transactions until EndTxn.

Wire Diagram

Response Header

message_size int32 · 4B

correlation_id int32 · 4B

FetchResponse v6

ThrottleTimeMs int32 · 4B

Responses array

Topic string

Partitions array

PartitionIndex int32 · 4B

ErrorCode int16 · 2B

HighWatermark int64 · 8B

LastStableOffset int64 · 8B

LogStartOffset int64 · 8B

AbortedTransactions? array

Records? records

ProducerId int64 · 8B

FirstOffset int64 · 8B

Schema & Example

Schema
{
  "ThrottleTimeMs": int32,
  "Responses": [{
      "Topic": string,
      "Partitions": [{
          "PartitionIndex": int32,
          "ErrorCode": int16,
          "HighWatermark": int64,
          "LastStableOffset": int64,
          "LogStartOffset": int64,
          "AbortedTransactions": [{
              "ProducerId": int64,
              "FirstOffset": int64
          }]?,
          "Records": records?
      }]
  }]
}

Example
{
  "ThrottleTimeMs": 0,
  "Responses": [{
      "Topic": "orders",
      "Partitions": [{
          "PartitionIndex": 3,
          "ErrorCode": 0,
          "HighWatermark": 284729,
          "LastStableOffset": 284729,
          "LogStartOffset": 284729,
          "AbortedTransactions": [{
              "ProducerId": 0,
              "FirstOffset": 150382
          }]?,
          "Records": null
      }]
  }]
}

Kafka Fetch Response Wire Format v6 — Binary Protocol Layout

What is Fetch?

Wire Diagram

Schema & Example