大致介绍
Topic是逻辑上的概念，而partition是物理上的概念，本来每个partition应对应于一个log文件，该log文件中存储的就是Producer生产的数据。Producer生产的数据会被不断追加到该log文件末端，为防止log文件过大导致数据定位效率低下，Kafka采取了分片和索引机制，将每个partition分为多个segment。每个segment包括：“.index”文件、“.log”文件和.timeindex等文件。这些文件位于一个文件夹下，该文件夹的命名规则为：topic名称+分区序号，例如：first-0。
实际查看
看一下实际是什么样的：
（1）启动生产者，并发送消息。
bin/kafka-console-producer.sh --bootstrap-server hadoop102:9092 --topic first
hello world
（2）查看 hadoop102（或者 hadoop103、hadoop104）的/opt/module/kafka/datas/first-1（first-0、first-2）路径上的文件。
ls
00000000000000000092.index
00000000000000000092.log
00000000000000000092.snapshot
00000000000000000092.timeindex
leader-epoch-checkpoint
partition.metadata
（3）直接查看 log 日志，发现是乱码。
cat 00000000000000000092.log
\CYnF|©|©ÿ"hello world
（4）通过工具查看 index 和 log 信息。
kafka-run-class.sh kafka.tools.DumpLogSegments --files ./00000000000000000000.index
Dumping ./00000000000000000000.index
offset: 3 position: 152
kafka-run-class.sh kafka.tools.DumpLogSegments --files ./00000000000000000000.log
Dumping datas/first-0/00000000000000000000.log
Starting offset: 0
baseOffset: 0 lastOffset: 1 count: 2 baseSequence: -1 lastSequence: -1 producerId: -1 producerEpoch: -1 partitionLeaderEpoch: 0 isTransactional: false isControl: false position: 0 CreateTime: 1636338440962 size: 75 magic: 2 compresscodec: none crc: 2745337109 isvalid: true
baseOffset: 2 lastOffset: 2 count: 1 baseSequence: -1 lastSequence: -1 producerId: -1 producerEpoch: -1 partitionLeaderEpoch: 0 isTransactional: false isControl: false position: 75 CreateTime: 1636351749089 size: 77 magic: 2 compresscodec: none crc: 273943004 isvalid: true
baseOffset: 3 lastOffset: 3 count: 1 baseSequence: -1 lastSequence: -1 producerId: -1 producerEpoch: -1 partitionLeaderEpoch: 0 isTransactional: false isControl: false position: 152 CreateTime: 1636351749119 size: 77 magic: 2 compresscodec: none crc: 106207379 isvalid: true
baseOffset: 4 lastOffset: 8 count: 5 baseSequence: -1 lastSequence: -1 producerId: -1 producerEpoch: -1 partitionLeaderEpoch: 0 isTransactional: false isControl: false position: 229 CreateTime: 1636353061435 size: 141 magic: 2 compresscodec: none crc: 157376877 isvalid: true
baseOffset: 9 lastOffset: 13 count: 5 baseSequence: -1 lastSequence: -1 producerId: -1 producerEpoch: -1 partitionLeaderEpoch: 0 isTransactional: false isControl: false position: 370 CreateTime: 1636353204051 size: 146 magic: 2 compresscodec: none crc: 4058582827 isvalid: true