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Kafka Metadata Response Wire Format v0 — Binary Protocol Layout

What is Metadata?

The first API every client calls after connecting, and re-called on NOT_LEADER or UNKNOWN_TOPIC_OR_PARTITION errors. A surge in Metadata requests signals partition leaders are moving around, typically during rolling restarts, broker failures, or reassignments.

Related Errors

LEADER_NOT_AVAILABLE · TOPIC_AUTHORIZATION_FAILED · UNKNOWN_TOPIC_ID

Wire Diagram

Response Header
message_size int32 · 4B
correlation_id int32 · 4B
MetadataResponse v0
Brokers array
Topics array
NodeId int32 · 4B
Host string
Port int32 · 4B
ErrorCode int16 · 2B
Name string
Partitions array
ErrorCode int16 · 2B
PartitionIndex int32 · 4B
LeaderId int32 · 4B
ReplicaNodes []int32
IsrNodes []int32

Schema & Example

Schema
{
  "Brokers": [{
      "NodeId": int32,
      "Host": string,
      "Port": int32
  }],
  "Topics": [{
      "ErrorCode": int16,
      "Name": string,
      "Partitions": [{
          "ErrorCode": int16,
          "PartitionIndex": int32,
          "LeaderId": int32,
          "ReplicaNodes": [int32],
          "IsrNodes": [int32]
      }]
  }]
}
Example
{
  "Brokers": [{
      "NodeId": 1,
      "Host": "broker-1.kafka.local",
      "Port": 9092
  }],
  "Topics": [{
      "ErrorCode": 0,
      "Name": "orders",
      "Partitions": [{
          "ErrorCode": 0,
          "PartitionIndex": 3,
          "LeaderId": 1,
          "ReplicaNodes": [0, 1, 2],
          "IsrNodes": [0, 1, 2]
      }]
  }]
}