（4）Consumer group: 每个consumer 属于一个特定的consumer group（可为每个consumer 指定 group name，若不指定 group name 则属于默认的group），同一topic的一条消息只能被同一个consumer group 内的一个consumer 消费，类似于一对一的单播机制，但多个consumer group 可同时消费这一消息，类似于一对多的多播机制
假设分区为 3, 即分三个分区0-2，副本为3，即每个分区都有一个 leader，再加两个follower，分区 0 的leader为服务器A，则服务器 B 和服务器 C 为 A 的follower，而分区 1 的leader为服务器B，则服务器 A 和C 为服务器B 的follower，而分区 2 的leader 为C，则服务器A 和 B 为C 的follower。
# Licensed to the Apache Software Foundation (ASF) under one or more # contributor license agreements. See the NOTICE file distributed with # this work for additional information regarding copyright ownership. # The ASF licenses this file to You under the Apache License, Version 2.0 # (the "License"); you may not use this file except in compliance with # the License. You may obtain a copy of the License at # # http://www.apache.org/licenses/LICENSE-2.0 # # Unless required by applicable law or agreed to in writing, software # distributed under the License is distributed on an "AS IS" BASIS, # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. # See the License for the specific language governing permissions and # limitations under the License.
# # This configuration file is intended for use in ZK-based mode, where Apache ZooKeeper is required. # See kafka.server.KafkaConfig for additional details and defaults #
############################# Server Basics #############################
# broker 的全局唯一编号，不能重复，只能是数字。 broker.id=0
############################# Socket Server Settings #############################
# 套接字服务器侦听的地址。如果未配置，主机名将等于的值 # java.net.InetAddress.getCanonicalHostName(), with PLAINTEXT listener name, and port 9092. # FORMAT: # listeners = listener_name://host_name:port # EXAMPLE: # listeners = PLAINTEXT://your.host.name:9092 #listeners=PLAINTEXT://:9092
# Messages are immediately written to the filesystem but by default we only fsync() to sync # the OS cache lazily. The following configurations control the flush of data to disk. # There are a few important trade-offs here: # 1. Durability: Unflushed data may be lost if you are not using replication. # 2. Latency: Very large flush intervals may lead to latency spikes when the flush does occur as there will be a lot of data to flush. # 3. Throughput: The flush is generally the most expensive operation, and a small flush interval may lead to excessive seeks. # The settings below allow one to configure the flush policy to flush data after a period of time or # every N messages (or both). This can be done globally and overridden on a per-topic basis.
# The following configurations control the disposal of log segments. The policy can # be set to delete segments after a period of time, or after a given size has accumulated. # A segment will be deleted whenever *either* of these criteria are met. Deletion always happens # from the end of the log.
