Analysis of Kafka's working principle and system framework

How Kafka works

Kafka is a distributed publish-subscribe messaging system that allows you to reliably deliver data between producers and consumers. It has high throughput, low latency and fault tolerance.

Kafka consists of the following components:

• Producer: A producer is an application or service that sends data to the Kafka cluster.
• Consumer: A consumer is an application or service that receives data from a Kafka cluster.
• Topic: A topic is a logical grouping of data stored in a Kafka cluster.
• Partition: Partition is the physical storage unit of the topic.
• Copy: A copy is a backup of the partition's data.

When a producer sends data to the Kafka cluster, the data is written to one or more partitions. Each partition has multiple copies to ensure data is not lost. Consumers can read data from any replica.

Kafka uses a mechanism called "offsets" to track where consumers read data. The offset is an integer that represents how much data in the partition the consumer has read. When a consumer reads data, it stores the offset in ZooKeeper.

If a consumer fails, it can be restarted from the last recorded offset. This ensures that consumers do not lose any data.

Kafka’s system architecture

Kafka’s system architecture is a distributed system composed of multiple nodes. Each node is an independent process, which can run on different machines.

Kafka nodes communicate through the TCP protocol. Each node maintains a copy of metadata, which contains metadata information for all topics and partitions.

When a producer sends data to the Kafka cluster, it first sends a request to the metadata node to obtain information about the partition to be written. The producer will then write the data directly to that partition.

When a consumer reads data from a Kafka cluster, it first sends a request to the metadata node to obtain information about the partition to be read. The consumer then reads data directly from that partition.

Kafka code example

The following is a simple example code using Kafka:

// 创建一个生产者
Producer producer = new KafkaProducer(properties);

// 创建一个主题
String topic = "my-topic";

// 创建一个消息
ProducerRecord record = new ProducerRecord<>(topic, "hello, world");

// 发送消息
producer.send(record);

// 创建一个消费者
Consumer consumer = new KafkaConsumer(properties);

// 订阅主题
consumer.subscribe(Arrays.asList(topic));

// 轮询消息
while (true) {
  ConsumerRecords records = consumer.poll(100);

  for (ConsumerRecord record : records) {
    System.out.println(record.value());
  }
}

This example code demonstrates how to use Kafka to send and receive messages. You can use this sample code as a basis to build your own Kafka applications.

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