Fetch request

As explained in Kafka Streams in Action, Second Edition

A fetch request is a Kafka client request that asks a broker to return records from a topic partition starting at a specified offset.

A fetch request is a Kafka client request that asks a broker to return records from a topic partition beginning at a specified offset. The consumer sends the request; the broker queues and processes it, retrieves a batch, and returns that batch in its response. Reading records does not remove them, change retention, or affect other consumers. section 2.3 section 2.10

A typical fetch flow is:

• The consumer specifies a topic partition and the offset from which it wants to read. section 2.3
• The broker takes the request from its request queue and fetches a batch of records. section 2.3 section 2.10
• The broker returns the batch to the consumer, which processes the records. section 2.3

Polling sales records

A Java KafkaConsumer subscribes to topics and repeatedly calls poll. A poll can return records retrieved by a new fetch request or records cached from an earlier call; returned sales records can then be logged or otherwise processed. section 4.3

Figure 2.3 Brokers handling requests from a consumer

Trace the broker-side handling of a consumer fetch request from request arrival through record retrieval and response. section 2.3

How Kafka Streams in Action, Second Edition covers it

How deep it goes

Explains request inputs, broker queueing, batch retrieval, responses, retention effects, and polling cache behavior without protocol internals.

Examples

Demonstrates broker diagrams and a Java sales consumer that subscribes, polls, and logs transaction values.

What it assumes

Introduces topics, partitions, and offsets as the surrounding concepts needed to understand fetch-request inputs.

What you can do after

Operate a KafkaConsumer that retrieves and processes topic records through subscription and polling.

How it connects

Connects KafkaConsumer, Kafka broker, topics, partitions, offsets, produce requests, and consumer clients.

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  Apache Kafka in ActionA fetch request is a Kafka protocol request for retrieving records from a partition.

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Related concepts

• offsetuses · An offset is a position or displacement measured relative to a reference point, such as within an ordered sequence, memory region, or layout.
• sink nodeused by · A sink node is a terminal or receiving component in a data or flow system that accepts incoming data, messages, or flow for consumption, processing, or storage.
• clientused by · A client is a person, organization, device, or software component that receives or uses a product, service, resource, or functionality provided by another entity.
• fetch.min.bytesconfigured by · fetch.min.bytes is a Kafka consumer configuration specifying the minimum amount of data a broker should accumulate before responding to a fetch request.
• Kafka brokeruses · A Kafka broker is a server process in an Apache Kafka cluster that stores records and handles producer, consumer, and other client requests.

This explainer was generated by Manning's knowledge graph from the text of Kafka Streams in Action, Second Edition. The section links point to the parts of the book it draws on.