---
title: Messages
description: Messages
weight: 2
tags: ['kafka', 'docs']
aliases:
keywords:
type: docs
---
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Messages consist of a variable-length header, a variable-length opaque key byte array and a variable-length opaque value byte array. The format of the header is described in the following section. Leaving the key and value opaque is the right decision: there is a great deal of progress being made on serialization libraries right now, and any particular choice is unlikely to be right for all uses. Needless to say a particular application using Kafka would likely mandate a particular serialization type as part of its usage. The `RecordBatch` interface is simply an iterator over messages with specialized methods for bulk reading and writing to an NIO `Channel`.