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obsidian-sync/日常学习/中间件/MQ/kafka/文件系统.md

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!Pasted image 20231126192023.png 不考虑多副本情况，一个分区对应1个日志，为了防止日志过大，kafka引入了日志分段的概念，每个LogSegment对应磁盘上的一个日志文件和两个索引文件（偏移量和时间戳）。

Log 中追加消息时是顺序写入的，只有最后一个 LogSegment 才能执行写入操作，在此之前所有的 LogSegment 都不能写入数据。为了方便描述，我们将最后 LogSegment 称为activeSegment ”，即表示当前活跃的日志分段。随着消息的不断写入，当 activeSegment 满 足一定的条件时，就需要创建新的 activeSegment ，之后追加的消息将写入新的activeSegment

一、消息格式

!Pasted image 20231126192854.png